Why did the united states fear texas expansion to california?

Conflict with Mexico began when the United States annexed Texas as a state in 1845.

Mexico claimed that the new border between Texas and Mexico was the Nueces River, while the United States contested the border was the Rio Grande.

Fighting began when a detachment of U.S. cavalry was attacked near the Rio Grande.

Zachary Taylor and Winfield Scott led armies to a series of military successes that culminated in the capture of Mexico City in 1847.

The 1848 Treaty of Guadalupe Hidalgo, forced onto the remnant Mexican government, ended the war and enforced the Mexican Cession of the northern territories of Alta California and Santa Fe de Nuevo México to the United States. The U.S. agreed to pay $15 million compensation for the physical damage of the war and assumed $3.25 million of debt already owed earlier by the Mexican government to U.S. citizens. Mexico acknowledged the loss of what became the State of Texas and accepted the Rio Grande as its northern border with the United States.

Explanation:

i believe that the answer to the question provided above is that  establishing smaller ethnic communities within larger communities  gives more chance for people to know each other more but this might lead to the  conflict between groups.

the first historical instance of china engaging in internationalism was during the han dynasty.[1] at the start of the han dynasty, the huns in the north were attacking the frontiers of han and trying to obtain riches. emperor wu of han wanted to gain an alliance with a country called dayuezhi so the two countries could join together and fight against the huns.[2] to obtain this alliance, emperor wu sent zhang qian to the west to establish economic and cultural connections.[2] history records that during the han dynasty there were four primary avenues of contact between china and europe. they included the northern land route, the central land route, the southern sea route, and the far southern sea route.[1] the most famous of these routes is the central land route, or the classical silk road, comprising a network of roads stretching from northwest china to the ports of syria and the black sea, which passed through the oasis of the turkestans and northern persia.[1] the silk road was significant for chinese emperors because it provided dominance over central asia by developing resources and provided new markets for the export of china's most valuable resources.[1]