How Anglo-Japanese treaty clauses redirect a world war

Would a surviving Anglo-Japanese Alliance force Britain to declare war on the United States after Pearl Harbor?

Not automatically; the treaty might instead oblige Japan to help Britain against Germany and Italy.

The Anglo-Japanese Alliance did not require automatic entry whenever either partner began a war. Its wider-war clause mattered when another power joined against an ally, so a Japanese attack on the United States alone need not oblige Britain to fight America. The same language creates the reverse possibility because Britain was already fighting Germany and Italy. If Japan continued to honour the treaty and had not aligned with Germany, it might feel bound to assist Britain. Japanese warships could then appear in the Mediterranean against Italy rather than in a war against the British Empire. The counterfactual turns on the alliance's defensive wording and the diplomatic changes required to keep it alive.