Well, despite your trollish behavior, Cow, I will answer you in a more hospitable manner.
Players should always worry about the naval supremecy of their opponents when playing an isolated nation such as England (Atlantic), America, ANZAC and Japan. If one allows the Americans to consolidate their forces, they will be too powerful for you to stop. If one attacks them from the outset you severely weaken the British navy in the Indian Ocean (they can hardly afford to replace a Battleship) and you virtually annhillate the American fleet. (What they can build and move to counter you is of no signficance, you can easy swat their new navy aside much like I just swatted your inhospitable, uncouth and vulger assault aside.)
America, with 50+ IPC a round at peace has 200 IPC to spend before entering the war licitely.
Add to that, 2 Submarines, 2 Destroyers, a Cruiser and 1 to 3 fighters that Japan will kill in round 1 and you see a serious dent being formed. (For the price of maybe 1 aircraft, I have now destroyed 57 IPC worth of naval and air forces. Yes, I got a fighter too, the one in the Philippines dies to the naval assault or the ground assault - either way, it dies.)
Now, America has 1 Carrier, 1 Battleship, 1 Cruiser, 1 Destroyer and 1 Transport in the water as well as 5 Fighters, 1 Tactical Bomber and 1 Strategic Bomber. Hardly enough to sink 3 Carriers, 4 Fighters, 2 Tactical Bombers, 1 Cruiser, 3 Destroyers and a Submarine.
In two turns, they can add 1 more cruiser to their pile, but that is the summation of their starting fleet and it is only 1% odds that America will win such an engagement when attacking, whilst Japan has 100% odds of winning a like engagement. And that is with no investment from Japan or America.
Now, it is obvious to anyone who has ever played this game that America will invest in the Pacific. However, I plan on J2 to take Hawaii and I do not believe there is a build in the world that America can do with 52 IPC to alleviate their odds. (add 2 more Japanese submarines and run the calculator yourself. Maybe I missed something?)
On J3, I have J2’s builds + 3 cover air patrol fighters to scramble as well as any other aircraft I put there to firmly establish that America is not in the war in the Pacific.
Essentially, on a round 1 strike, Japan has removed America from the game. It only remains to gobble up the rest of the Victory Cities needed to win by fiat. Honolulu, Sydney, Hong Kong, Manilla, Tokyo and the one in Kiangsu.
The real question is, why would anyone NOT attack America, England, France and China on round 1?