Why do presidents go to war? Students read about how five U.S. presidents justified wars with Mexico, Spain, Vietnam, Grenada and Iraq, then consider the merits of their arguments

The reading here and the suggested student activities that follow consider the controversies over the Iraq War in a wider context. The student reading briefly summarizes U.S. wars on Mexico, Spain, Vietnam, Grenada, and Iraq and quotes the reasons presidents gave for taking the nation to war. Following the reading are classroom suggestions aimed at helping students examine those reasons. More information about these wars (except the current one) should be readily available in history texts for student reference. For more on the current Iraq War, see "Iraq and the United States: The Road to War" on this website.


Student Reading:

The president calls for war

President Polk: War on Mexico, 1846

In 1846, President James K. Polk ordered General Zachary Taylor and his detachment of the U.S. army to cross the Nueces River in Texas and occupy the area that extends south to the Rio Grande River—a part of Mexico that had never before been claimed by Texas. By the end of March, Taylor's troops arrived in an area of cultivated fields and thatched-roof huts. The Mexicans living there had fled across the Rio Grande to the city of Matamoros. The soldiers began to construct a fort and set up cannons aimed at Matamoros.

On April 25 Mexican soldiers crossed the Rio Grande and wiped out an American patrol in the occupied area, killing 16 and wounding and capturing others. This news did not reach President Polk until the second week of May. He and his cabinet prepared a message to Congress, declaring, "...Mexico has passed the boundary of the United States, has invaded our territory and shed American blood upon the American soil..." and calling for a declaration of war. The House of Representatives voted 174-14 and the Senate 40-2 for war.

A first-term representative elected later that year, Abraham Lincoln, challenged Polk to identify the exact spot "upon the American soil" where American blood was shed. He argued that if you "allow the president to invade a neighboring nation whenever he shall deem it necessary to repel an allow him to make war at pleasure." Polk and most Congressmen paid no attention to Lincoln. But his constituents in Illinois did. They voted against his reelection in 1848.

Colonel Ethan Allen Hitchcock, a regiment commander under Taylor, wrote in his diary: "I have said from the first that the United States are the aggressors....We have not one particle of right to be here....It looks as if the government sent a small force on purpose to bring on a war, so as to have a pretext for taking California and as much of this country as it chooses....My heart is not in this business...but, as a military man, I am bound to execute orders."

After the U.S. defeated Mexico in the war, Mexico ceded Texas to the United States, down to the Rio Grande River.

President McKinley, War on Spain, 1898

In 1898 Cuban rebels had been fighting against Spanish rule for several years. Reports about the rebellion and exaggerated accounts of Spanish atrocities in Hearst and Pulitzer newspapers led many Americans to sympathize with the Cubans. And American business saw opportunities for profit if Cuba were free of Spain.

On February 15, 1898, the U.S. battleship Maine blew up in the harbor at Havana, Cuba, killing 268 American sailors. Spain denied having anything to do with the explosion. But a U.S. naval commission confirmed popular opinion among Americans that Spanish leaders were lying. The commission's work was brief and did not call upon experts in explosions and mines.

Early in April, the American ambassador to Spain reported to President William McKinley that Spanish leaders were willing to give Cuba its independence or even cede it to the U.S. On April 11, McKinley, "making only a casual and deceptive reference to the reassuring dispatch just received from Madrid," (Samuel Eliot Morrison, Oxford History of the American People, Volume 3) sent a message to Congress that concluded: "I have exhausted every effort to relieve the intolerable condition of affairs which is at our doors....I await your action." That action was a Congressional declaration of war.

The war was over in a few months. Spain was forced to surrender not only Cuba, but Puerto Rico, an island in the Marianas Islands and the Philippine Islands.

In 1975 U.S. Admiral Hyman Rickover concluded, along with other navy experts, that the cause of the Maine's explosion back in 1898 had in fact been internal and accidental. (Hyman Rickover, How the Battleship Maine was Destroyed)

President Johnson: War on Vietnam, 1964

For some years the U.S. had been supporting the South Vietnamese government in its civil war against the National Liberation Front, a South Vietnamese resistance movement that received support from communist-led North Vietnam and the Soviet Union. But the South Vietnamese regime was faring poorly in the war.

In 1964, U.S. President Lyndon Johnson authorized continuation of the secret Operation Plan 34A, which had first been approved by President Kennedy. The plan included using American planes with Laotian markings and patrols by American destroyers off the coast of North Vietnam in the Gulf of Tonkin to support South Vietnamese assaults on the North Vietnamese.

On August 2 the American destroyer Maddox was in the gulf gathering intelligence for the South Vietnamese regime when it was attacked by North Vietnamese torpedo boats, suffering minor damage. On August 4, the Pentagon reported that two American destroyers had again been attacked by North Vietnamese torpedo boats. This time, there was no damage to the destroyers.

The U.S. task force commander in the Tonkin Gulf cabled Washington that "freak weather effects," "almost total darkness" and an "overeager sonarman" raised doubts that there had been any attack by the North Koreans on August 4.
Nevertheless, the U.S. sent planes from its nearby carriers to hit North Vietnamese torpedo boat bases and fuel facilities. Squadron commander James Stockdale, who was one of the U.S. pilots flying overhead, later stated: "I had the best seat in the house to watch that event, and our destroyers were just shooting at phantom targets—there were no PT boats there... There was nothing there but black water and American fire power."

That night, President Lyndon Johnson, who was running for reelection, launched retaliatory strikes and went on national television to condemn North Vietnam's "unprovoked" attacks. Johnson informed Congress of the reprisals but not about Operation Plan 34A and not about the U.S.'s covert actions against North Vietnam. Despite the fact that there was no certain evidence of a second attack, he asked for a congressional resolution "to protect our armed forces."

On August 7, by an overwhelming vote, Congress approved Johnson's Tonkin Gulf Resolution, declaring that the Congress "approves and supports the determination of the President, as Commander in Chief, to take all necessary measures to repel any armed attack against the forces of the United States and to prevent further aggression."

The Tonkin Gulf resolution led to a widening of the war in Vietnam. By the war's conclusion in 1975, it would cost millions of Vietnamese casualties and the deaths of more than 50,000 American soldiers. It was a war the U.S. would lose. Several days after the Congressional resolution, Johnson commented to Undersecretary of State George W. Ball about the attacks on the two American destroyers: "Hell, those dumb, stupid sailors were just shooting at flying fish."

President Reagan: War on Grenada, 1983

U.S. officials had a wary eye on the tiny Caribbean island of Grenada ever since a 1979 coup led by Maurice Bishop, head of the New Jewel Party, a left-wing opposition group in Grenada's parliament. In 1983, after four years in office, Bishop was deposed by a hard-line communist faction supported by the Grenadian Army. The coup leaders established military rule. Six days later, Bishop was murdered.

With the installation of the new regime, the U.S. became even more concerned about Grenada's direction. On October 25, U.S. troops invaded Grenada. In a speech to the nation two days later President Ronald Reagan explained why. Fidel Castro's communist Cuba was behind the events on the island, Reagan charged, and "a Cuban occupation of the island had been planned." The number of Cubans there was "much larger" than original intelligence estimates of 400 to 600 and were "a military force" and not the construction workers they were supposed to have been.

Grenada, Reagan said, "was a Soviet-Cuban colony being readied as a major military bastion to export terror and undermine democracy" and that "we got there just in time." He also reported the discovery of three warehouses of military equipment with "weapons and ammunition stacked almost to the ceiling, enough to supply thousands of terrorists."

But the primary reason for the invasion, said the president, was that about 1,000 American citizens living in Grenada, many of them medical students, were in danger of being harmed or held hostage.

Castro, who had supported the Bishop government, denounced the new coup. The Cuban government estimated that there were 784 Cubans on the island. A few days after Reagan's speech, the U.S. State Department said that the Cuban estimate was about right. Then U.S. military officials on the island said most of these Cubans were workers, only about 100 "combatants."

No evidence was found that there was a terrorist training base on Grenada or that Cubans intended to take over the island. Reporters who examined the warehouses cited by the president said there were Soviet-made weapons and ammunition but that the warehouses were no more than half full and many of the weapons out-of-date. Whether the Americans were in danger remained in dispute after this war of a few days was over. A New York Times report stated, "Several assertions offered by officials as evidence that the danger justified the invasion have proven to be inaccurate." ( New York Times, 11/6/83)

President Bush: A Second War on Iraq, 2003

For months before the second U.S. war on Iraq President George W. Bush and members of his administration expressed great alarm about the danger they said Saddam Hussein's Iraq posed to the nation because of its weapons of mass destruction and ties to the terrorist group Al Qaeda, which had launched the attacks of September 11, 2001. Here are some of the president's pre-war comments:

January 28, 2003, State of the Union address:
"Year after year, Saddam Hussein has gone to elaborate lengths, spent enormous sums, taken great risks to build and keep weapons of mass destruction....Evidence from intelligence sources, secret communications and statements by people now in custody reveal that Saddam Hussein aids and protects terrorists, including members of Al Qaeda. Secretly, and without fingerprints, he could provide one of his hidden weapons to terrorists or help them develop their own."

February 8, 2003, in his weekly radio address:
"We have sources that tell us that Saddam Hussein recently authorized Iraqi field commanders to use chemical weapons—the very weapons the dictator tells us he does not have."

March 6, 2003, in a news conference on Iraq:
Saddam Hussein "provides funding and training and safe haven to terrorists, terrorists who would willingly use weapons of mass destruction against America and other peace-loving countries. Saddam Hussein and his weapons are a direct threat to the country, to our people and to all free people....The attacks of September 11, 2001 showed what the enemies of America did with four airplanes. We will not wait to see what terrorists are terrorist states could do with weapons of mass destruction....He [Saddam Hussein] is a murderer. He has trained and financed Al-Qaeda type organizations before, Al Qaeda and other terrorist organizations."

March 17, 2003, in a speech explaining why war was necessary:
"Intelligence gathered by this and other nations leaves no doubt that the Iraq regime continues to possess and conceal some of the most lethal weapons ever devised. The danger is clear. Using chemical, biological or, one day, nuclear weapons, obtained with the help of Iraq, the terrorists could fulfill their stated ambitions and kill thousands or hundreds of thousands of innocent people in our country or any other."

On the basis of Bush administration claims about Iraq's weapons of mass destruction and the likelihood that Saddam Hussein would use them against the U.S., the House of Representatives voted by a 196-133 margin and the Senate voted by a 77-23 margin to authorize the president "to use the armed forces of the United defend the national security of the United States against the continuing threat posed by Iraq."

A month after the U.S. invasion, American troops were in Baghdad. And on May 1, 2003, declaring major combat operations in Iraq over, the president said, "The battle of Iraq is one victory in a war on terror that began on September 11th, 2001, and still goes on....The liberation of Iraq is a crucial advance in the campaign against terror. We have removed an ally of Al Qaeda, and cut off a source of terrorist funding."

The Bush administration appointed David Kay to be its chief weapons investigator in Iraq. Kay was charged with locating the stockpiles of biological and chemical weapons that he said he believed Iraq possessed.

But after almost a year of searches, American investigators found no weapons of mass destruction. In January 2004, David Kay resigned his post. He stated: "It turns out we were all wrong, probably, in my judgment. And that is most disturbing."

On September 17, 2003, months after U.S. occupation of Iraq, President Bush said, in response to a reporter's question: "No, we've had no evidence that Saddam Hussein was involved with September 11."

There has been no conclusive evidence of any tie between Saddam Hussein and Al Qaeda. There is also no evidence to support the claim that Hussein would have given weapons of mass destruction to Al Qaeda - in fact, there is much evidence against it.


Classroom Suggestions

One well-known statement about the connection between war and politics was made by the 19th century Prussian general and philosopher of war, Carl von Clausewitz. He wrote: "War is a true political instrument, a continuation of political intercourse, carried on with other means."

A more recent scholar on war, Eliot A. Cohen, said that one of the first things professors teach in war colleges is that politics pervade war: "It's probably the most important thing to understand."( New York Times, 2/10/03)

In each call to war described in the reading, the president in question faced political considerations and pressures. President McKinley, for example, was under substantial pressure from the press and some members of his own party to war on Spain. In his announced determination for "regime change" in Iraq, President Bush appears to have had wider aims that included pressure for political change throughout the Middle East.

What political considerations affected each president's decision to go to war?


Divide the class into five groups. Ask each group to imagine itself a postwar Congressional committee charged with inquiring into one of the five wars outlined in the reading.

Committee members should

1) assemble information to answer the following questions

2) to prepare a report to the class of its findings and recommendations.

Questions for each Congressional committee:

  • What were the key events that led to war?
  • What information from intelligence and other sources did the president have about these events?
  • Was the president's use of this information appropriate? Why or why not?
  • What information did the president provide to the Congress and the nation?
  • Was this information accurate and sufficient for the Congress to give its authority for war? Why or why not?
  • What recommendations for any changes to future U.S. policy does the committee have? What are its reasons for these changes?


What questions do students have after reading each of the five summaries about a U.S. war?

Have students analyze each question and then decide which questions are worth further inquiry. See "The Doubting Game" section of "Teaching Critical Thinking" on this website for specific suggestions.


War on Mexico

  • Why did Colonel Hitchcock regard the U.S. as "the aggressors"? Do you agree? Why or why not?
  • How do you explain President Polk's decision to send U.S. troops to the Rio Grande River?
  • How do you explain his call for war on Mexico? the support he got from Congress? his ignoring Lincoln's "spot" resolutions?

War on Spain

  • Why did Americans sympathize with the Cuban rebels?
  • Why do you suppose the Maine was sent to Havana harbor?
  • How did Spain propose to settle its differences with the U.S.?
  • Why do you suppose President McKinley refused this settlement?

War on Vietnam

  • Why do you suppose that President Johnson did not inform Congress and the public about Operation Plan 34A?
  • How do you explain his call for a Congressional resolution "to protect our armed forces"?
  • Why do you think this call received overwhelming Congressional support?

War on Grenada

  • Why do you suppose President Reagan was concerned about events in Grenada?
  • In what respects were his public statements about what was happening in Grenada inaccurate?
  • How do you explain these inaccuracies?

War on Iraq II

  • Why do you suppose President Bush and his advisors expressed alarm about Iraq's danger to the U.S.?
  • Was the intelligence they received inaccurate? How do you know?
  • Did Bush and his advisors misuse—that is, exaggerate or misrepresent—the intelligence they had? How do you know?
  • If you had the authority to call for an investigation of how the U.S. went to war against Iraq for a second time, specifically what would you want to have investigated? Why?


  • Based on the reading, class discussions and inquiry, what conclusions do you reach about the circumstances that justify a president's asking the American people to go to war?
  • In an op-ed article, Richard Goodwin, a White House assistant to Presidents Kennedy and Johnson, writes, "Those now trying to figure out what went wrong before the war in Iraq should bear in mind a simple truth: we are more likely to 'know' what we want to know than what we don't want to know. That human flaw is built into the very process of making intelligence estimates." ( New York Times, (2/8/04) Discuss what implications you think Goodwin's statement should have for presidential decisions about war, referring to at least one of the case studies cited in the reading.


  • Letters to the president, senators and representatives on what students think about presidential decision-making on the Iraq war; or on what students think about the circumstances that justify a president's asking the American people to go to war.
  • A student-organized school assembly on presidential decisions to go to war. This could include 1) student summaries of their fact-finding inquiries; 2) a talk by an invited speaker (e.g., a political representative or aide) on the subject, with a student panel to question the speaker.



War on Mexico:
Samuel Eliot Morrison, The Oxford History of the American People, Vol. 2;
Benjamin Thomas, Abraham Lincoln;
Howard Zinn, A People's History of the United States

War on Spain:
Samuel Eliot Morrison, T he Oxford History of the American People, Vol. 3;
Howard Zinn, A People's History of the United States ;
Gilder Lehrman Institute of American History (online) on the blowing up the Maine

War on Vietnam:
Loren Baretz, Backfire; Theodore Draper, Abuse of Power;
Fairness & Accuracy in Reporting (, Media Beat article, 7/27/94 by
Jeff Cohen and Norman Solomon
"How Kennedy Launched His Secret War in Vietnam" by Dick Shultz, Fletcher School of Law and Diplomacy at Tufts University
"Battlefield Vietnam: A Brief History" by Robert K. Brigham, Vassar College

War on Grenada:
Raymond Garthoff, Detente and Confrontation; New York Times, 11/6/83
"The Invasion of Grenada" by Julie Wolf, PBS
"1979: Grenada leader Ousted by Coup," BBC (


This lesson was written for TeachableMoment.Org, a project of Morningside Center for Teaching Social Responsibility. We welcome your comments. Please email them to: