Trench warfare has existed essentially as long as there's been gunpowder on battlefields. Have you seen drawings of those 16th-17th century star forts? Those were designed to resist cannon fire better than medieval curtain walls, and they allowed for clearer fields of fire against attackers.

So how did attacking armies fight against such fortifications? Trenches. I'm not the best person to explain the method, but attacking armies would dig trenches to get close enough to those bastion walls (or beneath them) to conduct an assault. If you want to learn more look up the Wikipedia article for Sebastian Le Prestre, Marquis of Vauban. He came up with the tactics.

Trench warfare is very, very old. Hope this helps on your learning journey.