Passage: On 1 December 1918, the Act of Union, an agreement with Denmark, recognized Iceland as a fully sovereign state, an independent country in personal union with Denmark through a common monarch. The Kingdom of Iceland established its own flag and coat of arms and asked that Denmark represent its foreign affairs and defence interests on its behalf while retaining full control over its foreign affairs and defence. Iceland opened its first Embassy in 1920. The Act would be reviewed in 1940 and could be revoked three years later if agreement to continue it could not be reached.

Question: In what month did this agreement take place?
December