The entire population of the world could stand inside the area of the United Kingdom!
Each person would have 36 square meters or a space 6 meters by 6 meters (19 feet by 19 feet). The earth is no where near over-crowded, it is mis-used. More efficient irrigation, better use of sloped land for housing and terracing for argiculture would assist greatly with the worlds food needs. Better sharing and distribution with less waste and there would be no shortages.
People could work on resource management, not war machinery and destruction to resolve our population (food/water shortage, living space) concerns.