John Culver's biography of Henry Wallace, "American Dreamer" is a good read about this pivotal figure not much is otherwise covered. Wallace was born and raised a Republican, his father was Sec. of Agriculture for Harding and Coolidge, his grandfather a friend of Theodore Roosevelt, and he joined FDR's cabinet as a token Republican, by many rankings the only effective cabinet member as Secretary of Agriculture. Dwight Eisenhower's brother Milton was his right hand man there and would have likely helmed Ag or another key role in a Wallace administration. Jimmy Byrnes was a political enemy of Wallace's as were many of FDR's team and Sec. of Commerce Jesse Jones (also a Republican, Texan) was a quite hostile rival.
Wallace was an early advocate for the United Nations and likely would have defused the Cold War (a key USDA aide who was a Communist agent had helped filter what Wallace learned for years, just as Undersecretary of the Treasury Harry Dexter White, Undersecretary of State Sumner Welles, FDR Aide Lauchlin Currie, and others had manipulated FDR. As President Wallace would probably have been informed of what the Army Signal Corps had been working out of the Soviet embassies coded communications (Project Venona) which they'd broken in 1943, so that would make a sharp turn in Wallace's behavior...and probably trigger what's called "McCarthyism" by the left in expunging the 300 or so Soviet agents in the U.S. government at the time that the Army Signal Corps codebreaking identified. That would be a big POD.
Wallace had a significant interest in poverty alleviation, taking the the USDA into rural development, ending rickets, rural electrification and rural telephone service, etc. and that would be expected to be a significant part of his peace-time agenda, particularly in the Southeast which he'd toured extensively (and gotten his initial interest in ag research when George Washington Carver stayed at his family farm during Henry's boyhood.
Wallace was unusually enlightened about race for the era and the civil rights movement of the 1950's and 1960's would likely have been considerably telescoped with whatever power he assembled in Congress and the Supreme Court (potentially he would have been like Jimmy Carter in that respect, a moralist shouting among the amoral.)
Wallace spent a lot of time in South America during the war as Vice President working to keep those countries in the Allied camp and supplying key materials, teaching himself Spanish in the process. He'd toured Russia in the 1930's, albeit seeing Potemkin villages, but he'd still have been the first widely traveled President since Herbert Hoover and that would affect foreign diplomacy and especially trade and foreign aid in rebuilding after the war. Culver's book suggests much of what became known as the Marshall Plan for rebuilding Europe were actually Wallace's ideas, frequently presented and developed throughout the war (Wallace was Secretary of Commerce from 1944 on after being Vice President so by 1945 in OTL or ATL, he'd been at Cabinet level for 13 years continuously which is very rare experience.)
Wallace was a research scientist himself (genetics, botany, agronomy, soil science, statistics, economics) , Pioneer HyBrid seeds, the first hybrid crop seeds, were one of his side projects, and Herbert Hoover, Jimmy Carter, Thomas Jefferson are the only Presidents I can think of with substantial hard science training and lifelong interests. He would have collaborated more readily than Truman with Vannevar Bush in developing the federal labratories system, the National Science Foundation, DARPA, etc. after the war so that would have been a few years jump but with more funding and smarter management. Where that would have taken us is hard to guess.
Wallace would have been considerably more flexible than FDR about "unconditional surrender" in the waning months of the war, maybe a negotiated peace would have come about a few weeks earlier in Europe or in the Spring instead of the Summer of '45 with Japan. Wallace, unlike Truman, had been part of the Manhattan Project oversight committee since it's inception as well as heading raw materials sourcing for war production while Vice President so his perspective would have been far different from Truman who had seen wartime artilleryman service in France and spent World War II uncovering fraud in war production contracts/plants in the Senate. Wallace deferring to George Marshall on the war would have been more likely with the big POD's being dealing with post-war Europe and Uncle Joe whom Wallace had met in the 1930's while Truman of course had not.
I think the key POD question is if Wallace continued to be successfully managed by a Soviet handler on the policies towards Russia, as FDR had been, or would have somehow broke free (with the Army Signal Corps' irrefutable proof as opposed to say J. Edgar Hoover's suspicions.) He came extremely close even in the course of the Democratic National Convention to remaining FDR's VP for the 1944 election (Jimmy Byrnes probably did the most to torpedo that in last minute machinations as he had quite considerable informal power in the administration at that time with FDR's congestive heart failure leaving him able to work, sorta, a few hours a day by that point (see Thomas Fleming's excellent "The New Dealer's War."
It's odd that in both World Wars by the last year both Presidents Wilson and Roosevelt were nearly or fully incapacitated to an extent their staffs and families worked very hard to conceal despite it certainly being time for the Vice President to fully assume the office. Wrapping up the war with a drifting, unconscious President and advisors making the decisions, like the in movie "Dave", really makes you wonder about who made the decisions and how many POD's are buried there.
