Answer :
By 1916, "the war reached a stalemate". This was due mostly to the incarnation of trench warfare, which made traditional advancements extremely difficult for all side.
The correct answer is: "The war reached a stalemate"
In 1916, WWI had reached a stalemate, specially its Western front due to the trench warfare. Trenchs had been digged from the North Sea to the border between France and Switzerland. Although both sides attacked each other, no significant advances could be made. New military technology started to be tried, such as poison gas, air forces or tanks and eventually helped to break this stagnation.