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This map was is a continuation of the thought experiment started in the previous Steven Universe map, this time in an effort to visualize the World of Steven Universe as it would be seen around 1770, just before the American Revolution. As this is a world with a United States of America, a Mexico (Aqua Mexico?), and a Canada (with a horrible, evil green flag), it stands to reason that most of human history stayed pretty much the same until humans developed the technology to travel across the oceans, because without the commedy of historical accidents that preceded its discovery the Untied States of America and Canada would not have existed in the forms that are still pretty close to what we have in OTL. Now, this requires A LOT of suspension of disbelief, especially when you consider that great big ol' Sea in Siberia is right next to the heart of the Mongolian Empire (so were the Mongols still horseback riding raiders or did they become the Sea People 2.0?) So we're gonna assume that things didn't change until the late 15th Century.
SO: Here's a VERY rough timeline of events.
1494: Pope Alexander VI authors the Treaty of Tordesillas establishing a Papal Line of Demarcation that effectively defined the New World dominions of Portugal and Spain.
1499: Amerigo Vespuccia travels down the southern half of South America, confirming the Americas as new continents.
1512: Portuguese explorers land in Uruguay. The land is mostly grasslands, fed by the Uruguay and Sao Francisco river systems from the Espinhaço Mountains.
1520: Ferdinand Magellan becomes the first human in history to travel from Europe to Asia via the Panama Strait.
1532: Portuguese colonists land in northern Uruguay after Gold is discovered in the southern half of the Espinhco mountain range. Similar discoveries in the Pereira islands drive a mass migration from Portugal to the South Atlantic.
1542: Ruy López de Villalobos becomes the first European to land in Hawaii during his expedition to Asia, finally landing in what would become the Philippines in 1543.1607: The London Company's colonists land at Jamestown, Virginia
1763: The Treaty of Paris Divides Europe and America. The Dutch, who remained neutral during the war, establish an alliance with Spain to use Aqua-Mexico to access their colonies in the East Indies. Many Dutch colonists settle in the Guianas as a re-supply and layover port for vessels of the Dutch East India Company trading with Asia. Plans for a South African colony are abandoned after British and Portuguese relations continue to improve, homogenizing the Cape of Good Hope. The Namibian Channel comes to symbolize the Anglo-Portuguese alliance, while the Panamanian Strait symbolizes Spanish-Dutch alliance.
UPDATE: I made some changes based on the Crewniverse's postings of a more accurate depiction of the coastlines.
VIDEO: Matt Mitrovich (The Alternate Historian) made a video on Steven Universe's alternate timeline and this map. Take a Look