China is in a world of hurt because Japan invested heavily in its military.
The US, though a military power prior to 7-Dec-1941, is reeling from the attack on Pearl Harbor, and the fact that the Philippines have been overrun quickly by the Japanese with huge US causalities.
If the US had more FAST and BIG battleships as well as FAST and BIG Aircraft carriers, the US Navy could deal better with the superior Japanese fleet.
Though Japan at this point has more aircraft carriers in the Pacific at this time than the US, the lost about 1/2 their fleet of carriers at Midway when they were bush-wacked... This just happened a few months earlier...
Now the US was trying to halt the Japanese advance at Guadalcanal. The Japanese were close to cutting off shipping to Australia -- which would have also cut off supplying China...
Guadalcanal had many battles where the US casualities were unacceptably high -- because the US was ill prepared and ill equipped.
In perhaps the most important battle of Guadalcanal, the battleships Washington and South Dakota held off a Japanese task force.
Basically, the US could ill afford to have lost that battle as it would have meant that the Japanese would have control of the seas around Guadalcanal.
At this time, Japan was raping, plundering, and pillaging China.
The US was trying to help China fight the Japanese. The US was trying to help Great Britian and Communist Russia fight off Nazi Germany (and Italy).
The US had a two ocean war with not enough ships, men, aircraft, tanks or supplies.
But the economic might of the US was just starting to gear up for this war.
By the time the IOWA class battleships entered the war, the new FAST ATTACK CARRIERS, and lots of planes, tanks, and supplies, Japan was in a free-fall and Nazi Germany was in retreat on the Russian front and had lost North Africa.
Playing catch up in war means places get overrun and a vicious enemy (such as Communists or Nazis or Imperial Japanese) will torture/rape/pillage the CIVILIAN population that is overrun.
But then maybe you don't care about people being killed, tortured, sexually brutuallized, or having their homes destroyed and being taken off to concentration camps...
Maybe you read about conditions in concentration camps in Germany or Japan in World War II to understand the WHY of the US Military today.
Why does a small country like Israel have a large military?
I think it has something to do with the murder/slaughter of 5 million Jewish people in World War II.
I guess you don't have eyes to see what Communism/Nazism/Terrorism has done to the world -- making it a dangerous place...
Oh, about August 1942 -- by November 1942 Winston Churchill called it the "End of the Beginning"...
And the fact that she has her back to the sea, and there are people on three sides of her who would like to finish the job Hitler started.
Never again they say, and they mean it.