The German trained divisions were the elite of the infantry divisions in the Chiang Kai-Shek's National Revolutionary Army (NRA) trained under Sino-German cooperation until 1941. These divisions were active in the Chinese Civil War and Second Sino-Japanese War.
In 1927, after the dissolution of the First United Front between the Nationalists and the Communists, the ruling Kuomintang (KMT, or the Chinese Nationalist Party) purged its leftist members and largely eliminated Soviet influence from its ranks. Chiang Kai-shek then turned to Germany, historically a great military power, for the reorganisation and modernisation of the NRA.
The Weimar Republic sent advisors to China, but because of the restrictions imposed by the Treaty of Versailles, they could not serve in military capacities. Chiang initially requested famous generals such as Ludendorff and von Mackensen as advisors - the Weimar Republic turned him down, fearing that they were too famous, would invite the ire of the Allies, and would result in the loss of national prestige for such renowned figures to work, essentially, as mercenaries.
When Adolf Hitler became Chancellor in 1933 and disregarded the Treaty, the anti-communist NSDAP (the Nazi Party) and the anti-communist KMT were soon engaged in cooperation with Germany training Chinese troops and expanding Chinese infrastructure, while China opened its markets and natural resources to Germany. Max Bauer was the first advisor to China.