1750- A Russian merchant vessel is blown off course to California, they claim it for Russia and name it “Novyy Kavkaz”.
This is earlier than OTL Russia claimed Alaska, so any Russian claim is as ephemeral as Britain's Nova Albion. They can only enforce their claim with enough forts and men on the ground, and at that point Spain is the European power with the most control (although true control belongs to the American Indians)
More Russians at that date will likely translate to more guns for the Haida, Tlingits, and other groups they'd trade with in that area, and ideally an early potato introduction (although IIRC that was from the Spanish). Spain might have a shock when the California Indians have far more guns than they think.
1802- Britain sells Rupertsland to America.
Why should they, since it's producing plenty of fur? And why does the US want it since the US already has plenty of fur in their own lands and would rather buy (or god forbid conquer) the Louisiana Territory from France?
1815- America and Russia win. America annexes Florida and Louisiana, along with Bermuda and parts of the NWT along the 50th parallel to Oregon. Russia annexes most of Nevada.
The UK would never give away Bermuda without a serious defeat since it's an integral part of the Royal Navy's infrastructure. The most the US can get is the Bahamas and Turks and Caicos and maybe British Virgin Islands.
Russia has basically no power projection in Nevada and they wouldn't even want it (almost no furs and the mineral resources are unknown), they'd just want more of California like lands south of Fort Ross. At this point they run into the real problem of religion since most settlements are full of Catholics, Catholic priests, and missionised Indians who would be difficult for the Orthodox Russians to deal with (as they'll have problems setting up missions as they did OTL in Alaska). Odds are there will be pro-Catholic uprisings on the part of the Californios and Russian opponents like the British (who were an important force in Mexican California OTL) which will probably smash Russia, and all Russia really has is their very limited military force in the Americas and Indian allies (like the Aleuts) who certainly can't protect Russian interests in California.
American control over Oregon is pretty much nominal, the real power is in the hands of the Indians there who in turn are supplied by groups like the HBC who can cheat the treaty. And since the Indians there don't obey lines on the map (as OTL with many Salishan groups divided by the international border), the HBC and others groups can supply the Indians to deal with American operations there and also help them out.
1837- America wins and annexes Texas and occupies Cuba.
I don't think Spain is suffering these major defeats and not having the secession of their Latin American territories.
1861- The CSA declares independence, but doesn’t declare war.
War is inevitable since at some point the US will rightfully exert their rights of taxation over them and the CSA will oppose that with violence, and like OTL the US call for troops against the CSA which will provoke a crisis in border states like Virginia and Tennessee and likely result in their secession (and the creation of Unionist enclaves in West Virginia and East Tennessee) and thus the American Civil War occurs.
Really, by this time I think the British would've grabbed it all during the Crimean War since unlike OTL Alaska, this would include lands they have a huge interest in like the Fraser Delta, Vancouver Island, the Columbia River, and San Francisco Bay. And they'd grab Alaska with it. OTL, the British had a ton of interests in California (they were pretty much second to the Americans in Mexican California--something like half of California's non-Indian population in 1848 were Anglo-Americans, split between British and Americans) and of course had plenty of interests in Oregon Country and what is now modern Washington State and BC thanks to the HBC and their Indian allies.
1862- Mexico declares ware on the CSA in an attempt to reclaim their lost territory.
They were in no position to thanks to the French intervention, and even if the Hapsburgs weren't there, Mexico would've had yet another civil war or military coup that would've let the CSA protect Texas. The biggest lost would've been their New Mexico/Arizona campaign (it basically won't happen, which will affect the career of Kit Carson in the Civil War and also the infamous John Chivington of Colorado, murderer of the Cheyenne Indians at Sand Creek), and a lot of Texas CSA units defending against Mexico (and likely more against the Comanche which is interesting given their resurgence during the Civil War).
1885- America annexes Novyy Kavkaz.
How and why? I think a Russian territory in the Pacific Northwest (or basically everything north of the Bay Area) would be pretty well-settled by Americans and British (as Russia is a literal world away, across very nice Siberian lands to settle in). If it's an annexation, it's probably a partition. It can easily be a buffer state, like basically California north of the Bay Area/Central Valley and most all of Oregon, Washington, BC, Yukon, and Alaska, although I think the US will take the land south of the Columbia River and Britain north of the Columbia River.
1898- America wins and Annexes Puerto Rico and installs puppet states in the Philippines and Cuba. They annex Galveston from Mexico, along with a very small portion of Baja California.
No way is Mexico keeping Galveston that long since Anglo influence and their own inability to hold Texas would inevitably result in a successful Texas Revolution and US annexation. And why "a very small portion of Baja California", almost all of Baja California was empty until the mid-20th century, the US would have no reason not to grab it.
1918- Germany annexes Poland and puppets the Baltic States, Belarus, and Ukraine.
A Polish puppet state was in the works since Austria-Hungary would never allow Germany to take all of Poland and the Poles themselves would want something out of the effort they spent toward the war.