Answer:
Step-by-step explanation:
Honestly, the only reason I could find was what was in your assignment from yesterday.
The last sentence: "Mexico has passed the boundary of the United States, has invaded our territory and shed American blood upon American soil."
Texas was an independent territory, but had declared they wanted to join the United States, and so were considered part of the country pending officially being admitted as a state.
It's easier to argue that the US was unjustified in this case, truthfully
.