Complex sentence: The campaign itself starts 15 years after the formation of the alliance between the two factions, as the Tiberium Control Network is nearing completion, and the spread of Tiberium is finally stopped, bringing the light of optimism to the world's remaining population.
Split into simpler sentences: The campaign itself starts 15 years after the formation of the alliance, as the Tiberium Control Network nears completion. The spread of Tiberium is finally stopped, bringing optimism to the world's remaining population.