A classic authoritarian tactic: make being in the ingroup obviously better.

A positive boundary gradient.

People on the edge would rather be on the ingroup than in the outgroup.

Require people to corrupt themselves just a bit to join the ingroup.

That helps activate some cognitive dissonance, tying them tighter to the group.

Publicly pardon (or decline to prosecute) misdeeds by members of the ingroup.

This allows the members of the ingroup to act with increasing impunity.

Non-members of the ingroup will keep their heads down, lest they do something to attract negative attention from the ingroup.

As everyone keeps their heads down and minds their own business, trust degrades across society.

Blame any bad luck or negative consequences on the outgroup.

The authoritarian can change the definition of the ingroup at will.

This keeps even members of the ingroup constantly on their toes and focused on the authoritarian's whims.

The people who joined the ingroup are both powerful and powerless.

Entirely submitted to the authoritarians will.