Complex sentence: Four years later he was named ambassador to the neighboring Dominican Republic, where he forged an alliance with President Rafael Trujillo, until moving to Washington, D.C., to work as ambassador to the United States.
Split into simpler sentences: Four years later he was named ambassador to the neighboring Dominican Republic, where he forged an alliance with President Rafael Trujillo. He moved to Washington, D.C., after being appointed as ambassador to the United States.