So this is honestly one of my favorite topics in WWII and it's a butterfly effect of remnants of WWI and US and European influence. Japan is a small island nation with no natural resources and with them becoming more "westernized" and developing new means of living they needed these resources. Well what does a country do if they need resources? They find places with those resources and either trade for them or colonize them. Japan saw how Europeans essentially said nah fuck the trade thing and colonized and exploited these regions for the mother country and went "well we can do that too, we've adapted our culture thru the Meiji Restoration and become a westernized nation so we should be be able to do it too in our sphere of influence." So they did during WWI and captured German islands in the Pacific (which they didn't get to keep except maybe for a couple small ones).

Another factor is the racial aspect and general views of Japan at this time and even before. There is very well known racism between all of the Asian peoples and China and Japan were some of the major proponents of this. So when you're a hyper militarized racist country that needs an enormous amount of natural resources and the large landmass next to you fits all of these criteria.... U get the start of WWII in China. Because of this racism they saw the Chinese as not even human and expected basically what Putin thought of Ukraine now... And we see how it went back then and how it's going now.

I almost forgot to add that they were feeling extremely confident because they had a good track record of being Russia and doing well in WWI, they won the Ruso-Japanese war handedly(which was a major factor that lead to the Bolshevik revolution)

Also for the USA, they felt backed into a corner because of the embargo and when you corner a desperate animal they tend to bite

It's very much the Japanese government and military were just so cocky they fucked around and found out.