Source
https://www.google.com/search?q=trench+warfare&es_sm=119&tbm=isch&tbo=u&source=univ&sa=X&ei=TvliU_ScDs2PyASS1ICgCw&ved=0CEEQsAQ&biw=1256&bih=590#q=trench%20warfare&tbm=isch&facrc=_&imgdii=_&imgrc=gY5m4hsI6VwUOM%253A%3B-yxGVR3GHdS8aM%3Bhttp%253A%252F%252Fwww.dva.gov.au%252FaboutDVA%252Fpublications%252Fcommemorative%252Fhomefront%252Fimg_gallery%252FPublishingImages%252FP01424_002.jpg%3Bhttp%253A%252F%252Fwww.dva.gov.au%252FaboutDVA%252Fpublications%252Fcommemorative%252Fhomefront%252Fimg_gallery%252FPages%252FImage045.aspx%3B511%3B314

Throughout history, soldiers have used many different techniques  during war to protect and fight against their enemies . The use and combination of these techniques is called warefare. They pick the way they fight and protect themselves based on the type of land they are fighting on and the number of men they have in their army.