The purpose of the "Somme" was for the British to relieve pressure off the French army at Verdun. For many people the battle of the Somme symbolised the horrors of warfare in WW1. This one battle had a large affect on the overall casualty figures of WW1 and was one of the worst trench battles with trench diseases effecting many soldiers.
By the end of the battle, the British Army had suffered 420,000 casualties including nearly 60,000 on the first day alone. The French lost 200,000 men and the Germans nearly 500,000.