I've been thinking further about the long war model for the conflicts of the first half of the twentieth century, and now feel it may make more sense to think in terms of two long wars - a European long war which starts in 1914, subsides into a de facto ceasefire in 1923 with the conclusion of a peace treaty with Turkey, only to begin to smoulder again in 1936 with the Spanish civil war, the Saar, followed by the 1938 Anschluss and Sudetenland crisis.
1949 will still do as an endpoint as it marks the end of the Allied military government in Germany and the creation of the GDR and the Bundesrepublik.
In the east, we can posit a second long war, beginning in 1905 with the Russo Japanese conflict, or perhaps a decade earlier with the first Sino-Japanese war, which can be argued to mark the start of a sustained attempt by Japan to expand into Korea and China, and also to acquire territory in the Russian Far East.
That way, Japan's alliance with Britain, France and the US in the 1914-18 conflict makes sense as an attempt to acquire German concession of Kaitschou in China to add to Dalian, which it had acquired as part of the Russo Japanese war and to build a zone of control.
Equally the Japanese reluctance to withdraw their forces from the Amur and Primorye region in the wake of the Russian civil war and the Soviet establishment of a client state in Mongolia, their involvment in Xianjiang, and the Japanese encroachment in Manchuria and Mengjiang make considerable sense.
At the same time we can see Soviet policy aimed at countering Japanese influence and building an effective buffer between themselves and the Japanese area of control.
The endpoint remains 1949 with the establishment of the People's Republic of China, and which marks the end of the Soviet invasion and occupation of Manchuria.