There were two events in 1939 that provided context to the Pearl Harbor decision. First, there was a little battle in August on the border of Japanese occupied Manchuria and Soviet occupied Mongolia. Started a series of border skirmishes, ended with a semi-major battle, about 100K troops combined, 40K casualties (including wounded, missing and illness),tanks and aircraft. The Russians kicked ass.
The strategic plan had been, allied Germany and Japan would carve up the Soviet Union from both sides, satisfying the Japanese desire for empire. But, they got whipped by the Russians.
I had never heard of this until this weekend. Learning more history is so cool.
https://en.wikipedia.org/wiki/Battles_of_Khalkhin_Gol
And a month later, friend Germany signs a non-aggression pact with enemy Russia. These two factors caused them to look south for their empire dreams.
Then, with Barbarossa, friend Germany turns on their new friend Russia. Japan starts to wonder, will they turn on us? Or when? US Sec of State Cordell Hull was said to literally screamed this message to the Japanese ambassador to the US, imploring them to make peace with the US.
But, these things made them look to Indochina, Indonesia and the Phillipines for oil and empire. And the necessity to score a first round KO of the US fleet. Had the carriers been in port and got blasted, it might have worked, for a while at least.