Please select the word from the list that best fits the definition. Choose the best organizational aid for the use described below. Provides insight to cause and effect via ordered events:

ww1 weapons: tank. tanks were used for the first time in the first world war at the battle of the somme. they were developed to cope with the conditions on the western front. the first tank was called 'little willie' and needed a crew of 3.

the answer should be the fierce germanic invaders because they caused the western roman empire to decline.