noun
relative strength of political parties; distribution of parliamentary seats
Used in political analysis to describe how many seats each party holds in a legislature, or their relative influence.
選挙後の勢力分野を見ると、与党が過半数を維持している。
Looking at the distribution of seats after the election, the ruling party maintains a majority.
国会の勢力分野は、次の選挙で大きく変わる可能性がある。
The relative strength of parties in the Diet could change significantly in the next election.
Compound of 勢力 (power, influence) and 分野 (field, area). The exact historical derivation is uncertain; the term is used in modern political contexts.