participation in a war; going to war
taking part in a competition or contest
参戦した各国の損害は甚大だった。
The losses suffered by each country that entered the war were enormous.
彼のチームに参戦して初めて勝てた。
After joining his team, I won for the first time.
その国が戦争に参戦するかどうか注目されている。
There is great attention on whether that country will enter the war.