Covenant victories came early and often in the Human-Covenant war. Initially, humanity was completely unprepared and over-matched by the Covenant armada, and lost several colonies within only a few years. The UNSC managed to stem their losses through superior tactics, but this only delayed the inevitable. By the last years of the war, the UNSC fleets were severely weakened due to attrition, and the Covenant made major in-roads into the inner colonies. It was only the actions of John-117 and the Great Schism that ultimately allowed the UNSC to win at Earth.