China was at war with Japan in 1937. However, at that time, Germany had strategic and industrial cooperation with China on a rather large scale-namely, the German economy was benefiting from significant trade and orders from China, and a significant German contingent of military advisers were assisting the modernization and strategy of the Chinese army. At the same time, Germany and Japan were allied with the Anti-Comintern pact of 1936.

This created an awkward moment for Germany. Germany, having been deprived of its colonies, badly needed resources, such as rare earth minerals, tungsten, and antimony. China was a massive source of these materials, and was also on good terms with Germany as Germany was one of the major powers that wasn't interfering in China (partly due to their forfeiture of their concessions in China after WWI). As such, the two created a strong economic and military partnership that greatly increased China's warmaking ability, including the order of German equipment (such as the Stahlhelm, the German helmet), licensing of German equipment for Chinese factories (like the Gewehr 98k, which became known in China as the Chaing-Kai Shek Rifle), German reorganized and trained divisions, German military doctrine... the list goes on. There was a three-year plan enacted in 1936 that could potentially have made China's industrial war machine fully capable of repelling Japanese attack, had it been completed. As it was, China's military severely bled Japan's troops throughout the war, which in no short measure was due to the German cooperation.

The problem was that Hitler was planning to go to war soon with the Soviets. To that end, he needed an ally that had a military "now," as opposed to in a few years. To that end, he favored Japan, as their military and industry were already built up, as opposed to China, which was still somewhat decentralized and obsolescent. As a result, while they took their time about it, Germany eventually ended its cooperation with China after Japanese insistence, pulling out its military advisers and cancelling its economic agreements. They also recognized Japanese conquests, specifically that of Manchuko (Manchuria), culminating in the Tripartite Pact in 1940.

Sources:

Liang, The Sino-German Connection

Taylor, The Generalissimo: Chiang Kai-Shek and the Struggle for Modern China

Sure was in Yugoslavia (most particularly in Serbia). Now, Yugoslavia had two major resistance movements; the Chetniks of Draza Mihaljovic, Loyal to the Yugoslav Government in Exile in London, and the Partisans of Josip Broz Tito, who wanted a communist state. On top of that, there were occupation troops of Germany and Italy, the German installed Puppet regimes of the Independent State of Croatia led by Ante Pavelic and the Serbian government of National Salvation led by Milan Nedic. In addition there were a few more groups, namely the Russian Corps (founded from White Emigres who wanted to fight the spread of Communism), and the Chetniks of Kosta Penacac (who Abandoned Mihaljovic's Chetniks and pledged loyalty to the Germans)

Now, Not only were Mihaljovic and Tito's forces fighting against the Occupation and collaborationist forces, but they were also fighting amongst themselves. On several occasions fought alongside one another, whilst on others, both these groups even enlisted the help of the occupation forces to help fight the other. Mihaljovic's Chetniks on occasion they aligned themselves with the Italian occupation forces who offered them protection from the forces of the independent state of Croatia. Tito's partisans on several occasions aligned themselves with the Nazi occupation forces (that they were fighting) to fight the Chetniks. Whilst Initially Mihaljovic had the support of the British, Tito eventually gained their support and convinced the western powers to denounce the former as a collaborator.

Whilst Nedic's government was allied to the Nazis and fighting both Tito's and Mihaljovic's forces, Nedic, perhaps out of loyalty to the government in exile or recognising the threat of the Partisans, undertook several secret weapons transfers to Mihaljovic.

The Russian Corps pledged loyalty to the Germans in order to fight the Partisans under the condition that they would not fight Mihaljovic's royalist Chetniks, but fought them regardless.

Penacac's Chetniks initially fought against the occupation forces but later joined them. The Nazis and Nedic Government, recognizing their inefficiency, disbanded and imprisoned Penacac, who was then assassinated by men loyal to Mihaljovic.

TL DR: Everyone Fought with Everyone against everyone.