Conquering most of Europe might have been a possibility had the Kaiser seen the wisdom of avoiding a second front with Russia whilst exploiting, integrating & mastering new military technologies (i.e. tanks) early on in the conflict. Despite the fact that Germany (and to a lesser extent its allies) possessed a modern & effective army throughout the war it still failed to break the stalemate.

Conquering the world? Not a chance. First you have to overcome the Royal Navy which was as large as it was effective. Qualitatively speaking the Kriegsmarine might have been more modern & effective than the Royal Navy but it simply didn't have enough ships to do the job. Even if the Kriegsmarine managed to decisively defeat the Royal Navy the monumental task of projecting power overseas would have been extremely difficult as the US & Japan already had impressive navies of their own and would have certainly stepped up their respective naval programs to fill the vacuum.