Conversation so far:
what geographic feature was in the german sphere of influence in China in 1911?
Shandong Peninsula, Qingdao was a geographic feature in the german sphere of influence in China in 1911.
how was the sphere of influence lost for Germany in Shandong?
As a consequence of the First World War, Germany lost Qingdao and its sphere of influence in Shandong.
what happened after Germany lost Qingdao and its sphere of influence in Shandong?
After Germany lost Qingdao, The Treaty of Versailles transferred the leased territory to the Empire of Japan instead of restoring Chinese sovereignty over the area.
What was the Treaty of Versailles?
The Treaty of Versailles was the most important of the peace treaties that brought World War I to an end.

Question: when was the treaty signed?
Self-contained rewrite: When was the Treaty of Versailles signed?