Surface commerce raiding. Several German surface raiders, both cruisers and auxiliary ships had spectacular success during the Great War. But these were raiding the shipping of the greatest naval power, who had the units to run the German raiders down. In the end each of the raiders would be cornered and destroyed by British naval units.
Another hindrance to German commercial raiding was that the bulk of the nations of the world declared war against Germany. This allowed nations like Japan to seize the German Pacific colonies. German’s African possessions would follow soon afterward.
And the greatest obstacle to any German raiding strategy was in the realm of logistics. Unlike the age of sail or the nuclear submarines of the cold war, commerce raiding of the Great War era was very logistics heavy, with coal being a major shackle on the potentials for operations. To get around this the Germans would need a more successful logistics base for whips to resupply and repair battle damage. That would have taken a non European ally or a sympathetic neutral. Those were in short supply