The United States of America entered the Mexican-American War because Mexico claimed the Nueces River as its Northeastern Border, while the US claimed the Rio Grande River was the border between Mexico and the US. Also on the day that both U.S and Mexican Troops met at the Rio Grande and the Mexican Army opened fire, on April 25th, 1846, the Mexican American War began. Another reason on why America entered the war was because when Texas gained its independence from Mexico in 1836, the US declined to allow Texas into the Union. The Northern States were largely against Texas joining the Union because it would be a slave state, while the Mexican Government was encouraging border raids and warning that any attempt at annexation would lead to war.
The Mexican-American war was not justified. America entered the war with the strength of around 79,000 soldiers, while the Mexican force had around 18,000-40,000. The United States was prepared and had the economy to support the war, while the Mexican government was still forming. Another point is that President Polk was a believer in the widespread views of America “destiny” and Polk wanted America to be a continental nation. President Polk wanted the United States to stretch from the Atlantic to the Pacific, meaning his idea of the American Republic killed around 36,271 human lives just to see his dream come true.
When the Mexican war ended in the year of 1848, the Treaty of Guadalupe Hidalgo established the Rio Grande as the US-Mexican border and not the Nueces River. Another part of the treaty was that Mexico had to recognize the United States annexation of Texas into the Union. When this was all finished the US agreed to pay 15 million for all Mexican territory north of the Rio Grande, this added new states like California.
Several years after the Mexican-American war another crisis erupted, it was the threat of the annexation of the Southern states to create their own nation. This crisis would later result in war and be called the American Civil War. The Mexican-American war led to the Civil War by setting a ticking time bomb in place. The main issue of the Civil War was slavery, but with the addition of new states, the free and slavery states would be altered. When Texas became a state it became a slave state, and this would lead to another slave state in Congress. This lead to tensions between slave states and Free states, this heightened the debate over how Texas would be a Free State or slave
In 1850 a compromise came out named the Missouri Compromise this attempted to appease Southern Concerns about the shifting balances, but the nation was already headed to a Civil War. Many events happened after the 1850 Compromise like in 1852 Uncle Tom’s Cabin, 1854 – 1861 Bleeding Kansas, 1857 Dred Scott v. Sanford, 1859 John Brown’s Raid, and in 1860 Lincolns Election. Finally since the end of the Mexican American War, in 1861 the Battle of Fort Sumter happened, starting the American War.