The war with Mexico in the 1840s. Mexican War 1846
US Grant served in the Mexican War. His position was in the Quartermaster Corps. As an aside, Grant wrote later that he was against that war and saw it as a "land grab" by the US.
Union General William Patterson is most famous in his role in the US Civil War Battle of the First Bull Run. He had, however, served in earlier US wars. He was involved in the War of 1812, and also served in the Mexican War.
General Samuel R. Curtis graduated from West Point in 1831. In his graduating class of 33, he ranked 27th. Curtis was a Mexican War veteran and gained fame in the US Civil War Battle of Pea Ridge.
General Lee and General Grant
General Philip Sheridan fought as a Union general in the American Civil War
Was part of the Mexican War
Grant was the most successful Union general and Lee surrendered to him to end the war.
The Mexican War preceded the Civil War. Many of the Officers and Troops on both the Union and Confederate sides received their combat experience during the Mexican War.
Santa Anna.
Grant first went to war, as a Lieutenant in 1846 during the Mexican American War. He resigned his commission in 1854. In 1861 President Lincoln appointed him Brigadier General of Volunteers He ended the Civil War as General in Chief of the Union Army.
Zachary Taylor