Re: An elephant in the room
1 I last set foot in the UK in 1977. I have been an American citizen for literal decades now.
2 damn few Americans 'defended' Britain in WWII. There were a few volunteers, mostly in the RAF, and some serving naval personnel, notably 'observers' in maritime patrol aircraft (the first Navy Cross of the war was awarded to a USN officer serving as an 'observer' in an RAF long-range patrol aircraft which had a bit of an argument with a U-boat; the pilot and co-pilot were among the casualties, the 'observer' finished the attack, sank the u-boat, and brought the aircraft home, desapite being wounded himself) and the crews of USN ships on Armed Neutrality Patrol (USS Rueben James was sunk by a u-boat while on ANP off Iceland in September 1941; she was neither the first nor the last USN ship to engage u-boats while on ANP). The majority of the Americans in Britain were there to _attack_ Naziland; the 8th and 9th Army Air Forces, and the Army troops who went across the Channel. That noted bigot, Ernest King, pulled American naval forces (including the largest and most powerful ASW ships in the world, the 'Secretary' class cutters of the USCG) from the North Atlantic because he didn't want American ships to be under British command. He was fine with _Australian_ ships being under _American_ command, which lead directly to HMAS Canberra being sunk due to massive American incompetence; there would be a reason which there have been American ships named 'Canberra'. (Another Australian cruiser was part of the gun line at Suriago Strait; she was NOT the ship which caused the majority of American casualties in that action by raining fire down on an American destroyer, that would have been an American cruiser.)
3 Churchill and Roosevelt concentrated on the Nazis first because:
3a the Nazis were the most dangerous
3b Churchill & Roosevelt were (correctly) afraid of the consequences of leaving mainland Europe to be a private fight between the Nazis and the Soviets. Not least Churchill feared the consequences for morale among the various French, Dutch, Danish, Norwegian, Czech.and Polish units operating under British command; the Czech and Polish aircrews in the RAF were among the most effective, two Polish ASW ships were in the top 5 most effective, behind ships from Frederic John Walker's escort group, on the Atlantic; the Secretary cutters were the biggest ASW ships but not the best. Churchill _really_ didn't want to be seen as abandoning those men's countries.
3c Italy waa also in Europe, concentrating on Europe got a two-fer. (Actually, more, as Hungary, Romania, Finland, and Bulgaria were also Nazi allies; Japan had to be content with Thailand.)
4 no, Australia could not have been lost. Japan lacked the sealift to mount an invasion of Australia, just as they would have had serious problems getting to Hawaii. Japan could have _hurt_ Australia, badly, but actually taking it would have been a fantasy-land scenario right up there with the Nazis getting across the Channel.
5 Britain outlawed the slave trade in the first decade of the 19th century. One of the causes of the War of 1812 was British interference with American shipping attempting to run slaves across the Atlantic. Britain went so far as to declare that slavers were, for the purposes of law at sea, pirates, and subject to the same penalties as pirates when caught by the RN. That is, to be hung by the neck untill deasd, dead, dead. The US objected. Britain said 'come and stop us'.
5a slavery was abolished in British territories starting in 1833; there was to have been a period of 'apprenticeship' for 5 years, but mostly the now ex-slaves departed en masse. This had consequences; in the Caribbean, British planters imported, successively, workers from Madeira and the Azores (didn't work, is a major reason why there are a lot of people with Portuguese and Spanish names in Jamaica and the rest of the English-speaking Caribbean); Syria/Lebanon (didn't work; that's how Eddie Seaga's ancestors got to Jamaica, with major consequences in 20th century politics in the region); from China (didn't work, except to get lots of Overseas Chinese to places they would never have got on their own); and from India (didn't work, just got lots of Indians to Jamaica and especially Trinidad and Guyana; there's a reason why the West Indies cricket team had men with names like 'Ramadeen' and 'Kanhai' ) and finally to try to make things difficult for the ex-slaves and their descendants (didn't work; see further Paul Bogle and the Morant Bay Rebellion, and Alexander Bustamante and Norman Manley and the trades union movements. There would be a reason why politics in the region is dominated by parties which grew out of unions. The only thing more bolshie than a Jamaican cane cutter is a Guyanese cane cutter...) And, oh, in southern Africa the British abolition of slavery directly caused the Great Trek when the Boers went north to escape British tyranny and to keep their slaves. Meanwhile, the US fought a civil war to end slavery... and ton this day there are some who _still_ carry the battle ensign of the Army of Northern Virginia. Including idiots among those who stormed the Capitol building. (And they're doubly or even triply idiots; the actual ensign was _never_ the flag of the Confederacy, and was _square_, not rectangular. The idiots can't even get _that_ right.)