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Use the 2nd edition rules, FAQ, and setup. Also use the following official rules change (page 9 of the Rulebook):
The United States begins the game neutral. It may not declare war on Japan unless Japan first declares war on it or makes an unprovoked declaration of war against the United Kingdom or ANZAC. Following any such unprovoked declaration of war by Japan, the United States will receive an immediate one-time bonus payment of 30 IPCs, representing the total mobilization and transfer of military assets within the continental United States. However, if the United States is still not at war with Japan by the Collect Income phase of its third turn, it may declare war on Japan at the beginning of that phase. This is an exception to the rules for declaring war (see “Declaring War,†page 11), which may normally be done only at the beginning of the Combat Move phase.
There were two minor map changes in the 2nd edition. The first was to correct a 1st edition erratum (Sea zone 5 should not be adjacent to Korea. The border between sea zones 5 and 6 should meet at the border between Amur and Korea, leaving Amur still touching only sea zone 5 but Korea touching only sea zone 6.). The second was the combining of Yukon Territory and British Columbia into Western Canada, which should have no effect on game play.