You're right although the English 's technically isn't a case marker. You can see this because 's doesn't mark nouns, it marks whole phrases, in things like "th

You're right although the English 's technically isn't a case marker. You can see this because 's doesn't mark nouns, it marks whole phrases, in things like "the Queen of England's hat." Since it modifies phrases and not single words, while not being a word in its own right, it's a clitic and not a case marker. It does descend from the Germanic genitive case, though.