Mid-1840s:The United States engages in a brutal war in Mexico in an attempt to gain more land for America.

Late 1960s-Early 1970s: The United States engages in a brutal war in Vietnam in an attempt to stop the spread of Communism in southeast Asia.

Today: The United States engages in a war in Afghanistan, in an attempt to locate hidden terrorist groups.

Mid-1840s: The U.S.-Mexican War is started by President Polk with authorization from Congress. Polk says that Mexico's attack on American soil justifies the war, but the area of the attack is a disputed borderland, not officially recognized American soil. In addition, it is Polk's placement of American forces in this disputed borderland that prompts the Mexican army to attack.

Late 1960s-Early 1970s: Congress gives President Johnson unlimited powers to wage war in Vietnam, as the result of...