Final answer:
Trench warfare in WWI was caused by the development of new weapons like machine guns. This led to the construction of trenches to protect soldiers from gunfire. The effect of trench warfare was a stalemate on the Western Front, resulting in a long and costly war of attrition.
Step-by-step explanation:
The use of trench warfare in WWI was primarily caused by the development of new weapons and technology. One cause was the introduction of machine guns, which made it incredibly dangerous for soldiers to advance across open ground. This led to the construction of trenches as a defensive measure to protect soldiers from gunfire and artillery.
An effect of trench warfare was the stalemate on the Western Front. The trenches created a static and fortified front line that was difficult to break through. This resulted in a long and costly war of attrition, with both sides heavily entrenched and neither able to gain significant ground.
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