Join is defined into three definitions:
PARTICIPATE IN and TAKE PART IN
PARTICIPATE (usually used with preposition IN), is defined as BE INVOLVED or TAKE PART. Similar to PARTICIPATE, TAKE PART IN has the same meaning. TAKE PART IN is the idiom version of the phrasal verb PARTICIPATE IN. They both are interchangeable.
Basically, JOIN, PARTICIPATE IN, and TAKE PART IN are all interchangeable when the purpose is to get involved. However, JOIN may also be used to tell an INITIAL ACTION of becoming part of some event; used for non-physical action (e.g. I joined the football game, but I just watched the game) or before the non-physical action. On the other hand, both PARTICIPATE IN and TAKE PART IN refers to physical actions one is involved in (I took part in the basketball game and I sweated like crazy).
Well, that is all of my explanation about the difference of those three. I hope it helps and you won't be confused to use them anymore. Cheerio!