the stalemate lasted so long because it was nearly impossible to attack without suffering major losses... umm... the tactics of WWI was called trench warfare in simple terms i dig a line miles long and you dig a line for miles long and shoot at each other till your officer thought you had enough men then you climbed out of your hole and marched towards thousands of rifles pointed at you and then after the battle considering if anyone survived and you did actually take over the enemy trench you would need replacement troops to fill in for the thousands of dead soldiers