Why Treaty of Guadalupe Hidalgo is important?

The Treaty of Guadalupe Hidalgo ended the US-Mexican War in 1848. From this treaty the United States gained 500,000 square miles of territory and emerged as a major world power. However, the United States was rather arrogant while making this treaty, which kind of spoiled Mexico and American relations. It is one of the oldest treaties that is still in effect with Mexico and the United States.