What is the fine-grained topic of the following text: But more significant to rugby in the East, was that after a last full season 1939, the ERU would not number as many as ten teams again until the NYRFC’s 1960 Thanksgiving Seven-A-Side tournament. Only return the topic.
The historical development of rugby in the East, specifically focusing on the Eastern Rugby Union (ERU) and New York Rugby Football Club (NYRFC).