Was the United States justified for declaring war on Japan? Explain in 3-5 complete sentences.

Yes

Explanation:

The USA was completely justified in its declaration of war against Japan as the Japanese during the Pearl Harbor attacks, killed  thousands of American Sailors. Such an action was in of itself was a declaration a war against a sovereign country making the US's decision to declare war was completely justified. This threatening of  US sovereignty by Japan was ample reason to declare war and was certainly justified.

it affected it because the kingdoms (with trade) slowly got richer and richer.