To make something (or someone) more heavily armed with weapons, especially in preparation for battle, is to militarize it. If a country militarizes, it's preparing for war or violent conflict.
A nation that is militarizing might assemble and train various armed forces (like the Army and the Navy), ready tanks to defend an area, or send ships to sail into battle. When you militarize a police force, it starts to look more like an army. And if a company militarizes its personal security force, that may mean arming guards with guns and dressing them in bulletproof vests. The verb militarize comes from military and its Latin root miles, "soldier."