cosmos-sdk/docs/spec/staking/end_block.md

End-Block

Validator Set Changes

The Tendermint validator set may be updated by state transitions that run at the end of every block. The Tendermint validator set may be changed by validators either being jailed due to inactivity/unexpected behaviour (covered in slashing) or changed in validator power. Determining which validator set changes must be made occurs during staking transactions (and slashing transactions) - during end-block the already accounted changes are applied and the changes cleared

EndBlock() ValidatorSetChanges
    vsc = GetTendermintUpdates()
    ClearTendermintUpdates()
    return vsc