Alaskan panhandle dispute;
Guatemala's,
Colombia's (in that dark bluish grey part),
Costa Rica's (I can't find the source for the middle one tho) and Venezuela's weird old borders; corrected that British Guiana-Brasil dispute, Republic of Counani correction and
"variant" border; added Caprivi strip, old German EA border and old Oubangui-Shari border (also corrected the northernmost British Cameroon since in fact there was a Quadripoint). Added RK Ostland and Ukraine borders, Ukranian and Belarusian borders after the partition of Poland, republic of Central Lithuania, most of the Belarusian People's Republic (I'll do the rest after more of Russia is finished), Socialist Soviet Republic of Byelorussia and Lithuanian–Byelorussian Soviet Socialist Republic (I don't know if Veyshnoria counts, but I added the borders in beige anyway)
I dunno, like, I know that modern internals aren't always following historical borders, but I feel like there should be less conflict between the two base-maps, especially in Poland and Germany.
It was mostly the nazis fault, who changed those old provinces of the Weimar Republic and messed up Poland so badly (that and the messed up times in eastern Europe during WW1)