Shmita and Exile

“Exile comes to the world on account of idol-worship, sexual promiscuity, murder and the failure to leave the land fallow on the sabbatical year.” – Pirkei Avot

What do idol-worship, sexual promiscuity, murder, and failure to leave the land fallow in the sabbatical year have in common?

Why is exile a punishment/consequence?

What is “exile”?