The Peninsular campaign was notable for the development of another method of warfare which went largely unnoticed at the time, but would become far more common in the 20th century. That was the aid and encouragement the British gave to the Spanish to harass the French behind their lines which led them to squander most of the assets of their Iberian army in protecting the army's line of communications. This was a very cost effective move for the British, because it cost far less to aid Spanish insurgents than it did to equip and pay regular British army units to engage the same number of French troops.