By the eighth century BCE, Israel had divided into two kingdoms and the Northern Kingdom had fallen into idolatry, injustice and violence. Hosea was a prophet sent to the Northern Kingdom just before the Assyrians destroyed it and sent ten tribes into exile.
Hosea's life and prophecy was conducted through his marriage to a prostitute. In this, he mirrored God and His marriage to Israel. One can see God's heartbreak as the beloved Ephraim descended from the heights to which it had been raised after the Exodus.
The final straw in God's eyes was when the priests and leadership, the government of Israel, began to prey on the people. The rampant injustice was too much for God any longer to tolerate.