JMA posted:
One thing you can be sure of is that the US will never take on the Russians or the Chinese. That you can take to the bank.
I accept international politics is far from predictable, but if anything the USA since 1945 has been quite an unpredictable 'policeman'. As a certain Mr Saddam Hussain discovered after invading Kuwait.

Long time since I studied pre-1939 (for non-US) or pre-1941 (for the USA) international affairs, but I'd wager Hitler decided the US would never take Germany on. Less sure whether Tokyo thought the USA would do much beyond shouting and having the Burma Road (to Nationalist China) considering by 1941 Japan had been at war in China since 1937.

Having listened to a discussion on BBC radio this week on China, it appears they have enough internal issues to face / avoid and whilst maritime skirmishing in the South China Sea causes concern does it really "ring alarm bells"? Not to overlook Taiwan, a potentially far bigger prize for China if peacefully reunited (larger than Hong Kong by a significant factor IIRC).