Final answer:
Germany experienced rapid success in the first months of the war due to their ability to defeat the Russians and launch a surprise attack on France. However, their advance was halted by the French and British forces.
Step-by-step explanation:
The rapid success experienced by Germany in the first months of the war can be attributed to several factors. Firstly, the German army was able to stop and defeat the advancing Russians on the eastern front. Additionally, the Germans invaded and occupied Belgium, allowing them to launch a surprise attack on France. However, despite their initial success, the German advance was halted by combined French and British forces, leading to a stalemate on the western front.