[DesertRhino]

“We went to war over the Republic of Texas applying to the United States for statehood and because Mexico would not sell us California. How is that agressive Mexican moves?”

Texas won independence 10 years earlier. Although defeated, Mexico never relinquished their former claim. Texas claimed to the Rio Grande as they applied for statehood.
Mexico claimed up to the Nueces.
The war established that Mexico did not own that strip and nailed down the limits of Mexican claims.

[Old Teufel Hunden]

"The war established that Mexico did not own that strip and nailed down the limits of Mexican claims."

If that were the only thing it was about (and I did mention it), why did we get Arizona, New Mexico and California? President Polk tried on several occasions to purchase California from Mexico. They didn't want to sell it. That is also one of the major causes of the war.