Texas was once part of Mexico. After Texas became an independent republic, leaders in the United States wanted to add it to the country. When the United States annexed Texas, Texas officially became part of the United States in 1845.

This change made Mexico angry. Mexico still believed Texas belonged to them. Mexico also disagreed about the border. The United States said the border was the Rio Grande. Mexico said the border was farther north at the Nueces River.

Why Problems Grew

This border argument caused more and more tension between the two countries. Tension means growing anger or disagreement. Each country made a claim about where the border should be.

Another idea also pushed the United States westward. It was called Manifest Destiny. This was the belief that the United States should spread across North America. Because of this belief, many Americans wanted more land in the West.

The fight over Texas was not only about one river. It was also about land, power, and expansion. As both sides stood by their ideas, the conflict grew worse.

The War Begins

In 1846, fighting broke out between the United States and Mexico. This conflict is called the U.S.-Mexican War. It lasted from 1846 to 1848.

The war began after troops from both countries moved into the disputed land between the Nueces River and the Rio Grande. After fighting started, the United States declared war. Mexico fought back, and the war spread into other areas.

How the War Ended

In 1848, the war ended with the Treaty of Guadalupe Hidalgo. A treaty is an agreement between countries. This treaty said that the Rio Grande would be the border between Texas and Mexico.

The treaty also gave a large amount of land in the West to the United States. This was a major change for both countries. Mexico lost land, and the United States grew much larger.

Why This Matters

The annexation of Texas, the border dispute, and Manifest Destiny all helped lead to war. These events changed maps and changed people’s lives. They also shaped the future of Texas and the United States.

Today, this history helps us understand why borders matter and how disagreements between countries can lead to war. It also shows how one decision, like adding Texas to the United States, can lead to many other changes.