Starting in 1900 everything goes the same up to WWII, when the Soviets refuse to declare war on Japan the US and British together invade Korea. Winston Churchill is asked by Prime Minister Atlee and President Truman to go to Moscow on behalf of the Western Alliance and inform Stalin the previous agreement over the division of Korea was now void. Stalin obviously aint happy but does not want to provoke the wraith of his former allies by killing Churchill or declaring war. He insists on something for Soviet blood spilled by the Japanese in 1939. Churchill is able to secure the southern half of Sakhalin Island only for Stalin.
Korea is re-partitioned between Britain, US and France. With Britain getting most of North Korea, the US getting South Korea, and France getting a small part of Northeast Korea. The Three governments unite the Peninsula in 1947 as a Republic. By 2004 Korea is a unified Asian Tiger with the whole peninsula enjoying a greater success than SK enjoyed in OTL. It is a staunch ally of the US in the Cold War sending troops to fight in Vietnam (a greater amount than OTL), Desert Storm in 1991, Afghanistan 2001-present and Iraq 2003.