Two key factors that contributed to Germany's initial success during World War I were its military strategy and its ability to effectively mobilize its resources.
Military strategy: Germany's Schlieffen Plan, which was a strategy for a quick victory against France, was initially successful. It involved a rapid invasion of neutral Belgium and a sweep through northern France, which caught the French off guard and allowed the German army to quickly advance deep into French territory.
Effective mobilization: Germany was able to quickly mobilize its resources, including its industrial base, to support the war effort. This allowed the German army to be well-equipped and supplied, which was an important factor in their initial military successes.
Additionally, Germany had the advantage of fighting on only one front which allowed them to concentrate most of their army on the Western front and defeat Russia in the east.