What was James K. Polka'd justification for war against méxico? Why did many northerners saw the war as an excuse to expand slavery?

The correct answer to this open question is the following.

Although there are no options attached, we can say the following.

James K. Polka'd justification for war against México was to expand the imperialistic ideals of the United States acquiring the territory of California and Texas. That is why he offered Mexico to buy those territories but the Mexican government thought it was an insult to the country and did not accept. President Polk wanted to fulfill the Manifested Destiny of the US.

That represented the beginning of the Mexican-American War that ended with the signing of the Treaty of Guadalupe-Hidalgo. That is how the US ended up getting the territories of California, Arizona, and Texas.

Many northerners saw the war as an excuse to expand slavery because with more and vast territory in the hands of the United States, more land to be exploited, more raw materials, and natural resources to make a profit and use slaves to farm the lands.  

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