France and England were incredibly wealthy and powerful in 1914 because of the vast colonial expansion of the 19th century.
Because of earlier French occupation, historic religious disputes and competing centers of power, Germany was late to the game of becoming a unified national state and also way behind on colonial expansion.
Germany was belatedly trying to become a world power and a naval power. However, Germany was already becoming the world's leading industrial power.
Geography made it difficult for Germany to compete navally and colonially, but geography combined with industry also gave Germany great advantages as a continental military power.
France and England did not want Germany to compete with them on the world stage and Russia did not want Germany to expand eastward.
Germany and Austria-Hungary saw a fullscale war as an opportunity to rebalance the global system - by conquering the Low Countries and France, Germany could demand that France turn over part or all of its colonial empire to Germany, enabling Germany to not only become a colonial power but establish enough global ports to become a naval power to rival Britain.
In a nutshell - WWI was about Germany making up for a century of lost time and lost opportunities in what they thought would be a one-year military campaign - the model being the Franco-Prussian War of 1871, this time on steroids.
Thank you.