The answer to this question is that weapons in warfare have changed over time because they have become much more technologically sophisticated and much more deadly over time. Just consider the fact that early wars between civilizations were conducted using swords, spears, and bows. Wars today are conducted using such weapons as missiles fired from airplanes (manned and unmanned) and ships, tanks, cannons, and machine guns. This shows just how much weaponry has increased in sophistication and power.
Ever since history began, people have engaged in warfare. Since people have been fighting constantly, they have also been in a constant search for new weapons that would allow them to have greater power than their enemies. They have tried to find better weapons so that they could kill their enemies without being killed themselves. This has led to a process in which weapons have become much more powerful and much more technologically sophisticated. We have gone from arrows made of wood and stone or metal that could each kill one person to having bombs that can easily kill (even when they are just conventional bombs and not nuclear weapons) hundreds of people at once. This is how weapons used in war have changed over time.