The Mexican War 1846-48 involved unpaid debts to Americans, a desire for West coast territory, and the issue of Texas whose independence was not recognized by Mexico. The Southern boundary was in dispute also.
Polk’s administration wanted to provoke a Mexican attack. Congress actually censored President Polk for that action. In the 1854, the President acted to protect American lives and property abroad in Nicaragua. American forces burned down every building in Graytown. The U.S. Government defended this action. In the 1890s many Congressmen wanted war with Cuba, but the President did not want it.
President McKinley dispatched 5,000 troops to China without Congressional approval to support the Boxers in their rebellion. Under Wilson, the League of Nations caused controversy because it appeared to obligate the United States in every breakout.
The President does not have broad discretion at his disposal. But, the modern view is that there are few restraints. The Korean War 1950-53 was the watershed of this idea. Truman committed American forces with no declaration of war by calling it a police action only.
Lecture 10 of 10 from Thomas Woods' The Truth About American History: An Austro-Jeffersonian Perspective.