Complex sentence: It involved 15,000 American, Afghan, British, Canadian, Danish, and Estonian troops; constituting the largest joint operation of the War in Afghanistan up to that point and aimed to remove the Taliban from Marja and eliminate the last Taliban stronghold in central Helmand Province.
Split into simpler sentences: It involved 15,000 American, Afghan, British, Canadian, Danish, and Estonian troops; constituting the largest joint operation of the War in Afghanistan up to that point. Aiming to remove the Taliban from Marja and eliminate the last Taliban stronghold in central Helmand Province.