仗original means weapons, and its extended meaning is battle or war. It’s a noun. Usually we use 打仗 to express war or fight a battle, and we can use 胜仗 or 败仗 to show win or lose.
战 means war, it can be a noun, also can be a verb. When it uses as a verb, it means fight a battle.
We always use 战争 to express war, but it’s greater. For example, we use 第一次世界大战 to express World War I.
Hope this expression can help you.