How did Germany prevent the US from shipping goods to the other Allied countries?

Anagnos: . . it will no doubt be difficult for you there, annie. but it has been difficult for you at our school too, hm? gratifying, yes, when you came to us and could not spell your name, to accomplish so much here in a few years, but always an irish battle. for independence. (he studies annie, humorously; she does not open her eyes.) this is my last time to counsel you, annie, and you do lack some – by some i mean all – what, tact or talent to bend. to others. and what had saved you on more than one occasion here at perkins is that there was nowhere to expel you to. what do anagnos's words reveal about annie in this excerpt