While the U.S. Army has constructed many buildings for urban warfare training, all of the structures are based on houses and commercial structures typically found in the West. But the rest of the world, where most of the fighting takes place,  has different ideas on how buildings should be laid out. This was learned the hard way in Afghanistan and Iraq. Actually, it was also noticed in Somalia in 1994, but this had little impact on how training facilities were designed. The techniques for fighting in Western style buildings are quite different than those that work in Middle Eastern residences (that often  feature a central courtyard and fewer corridors). There were other problems as well. American infantry have charts showing the impact their weapons have on various kinds of building materials. But in Afghanistan and Iraq, many structures were made of mud brick, or other unfamiliar materials. Little details like typical building layout and what they are made of can mean the difference between life and death for the troops.