I'd go back to the early 1880s, ˝invent˝ moonclips, and use some of the profit to hire an assassin and get rid of Friedrich Wilhelm Viktor Albert before he has a chance of becoming the next Kaiser. Moonclips could easily give revolvers an edge over early autoloaders, keeping them in military service a lot longer. And without Wilhelm II Germany wouldn't ruin the British-German relationship, resulting in a Cold War with Britain, Germany and Austria-Hungary on one side, and the Franco-Russian alliance on the other side. This would abort the First World War, because the former could easily curbstomp the latter. Without the First World War Britain would have no reason to stop building battleships and battlecruisers, constantly escalating their designs. Britain in those times had a strong alliance with Japan, so the Japanese Navy would follow suit, trying their hardest to build and then constantly rebuild their 8-8 fleet. The Anglo-Japanese alliance and the US of A were quite suspicious of each other, so America would most likely respond to this by building their own fleet of increasingly larger and more powerful battleships. By the 1930s we'd live in a world filled with revolvers and battleships!