I want to know the answer to the following question:
When did the First Council of Nicaea rule that Easter be celebrated by all Christians?
All the background I'm provided with is that "Although a recommendation of the First Council of Nicaea in 325 specified that all Christians should celebrate Easter on the same day, it took almost five centuries before virtually all Christians achieved that objective by adopting the rules of the Church of Alexandria (see Easter for the issues which arose).". Is that enough to answer the question?
Answer: yes