i have an idea for what to do with a POD of 1450 or so...
the gist is that Spain doesnt unify, but leaves three seperate kingdoms; Portugal, Castile, Aragon. from there butterflies take effect. the next major issue is American Colonialism. the OTL US Eastern Seaboard (thirteen colonies + more) are colonized by multiple nations due to a treaty. however a later war forces this peace down the drain, and destabilizes the american colonies way earlier. they declare and gain their independence by, or prior to 1770. hopefully by 1750 but '70 is do-able. and then the line of presidents changes...