The invasion was precipitated by the need for German forces to reach Greece to save Italian forces, which were failing on the battlefield against the Greek armed forces. Upon rescuing Italian forces in Greece and having conquered Yugoslavia and Greece almost single-handedly, Hitler became frustrated with Mussolini and Italy's military incompetence. Germany improved relations with the Ustaše and supported the NDH claims to annex the Adriatic Coast in order reduce Italy's planned territorial gains. Nevertheless, Italy annexed a significant central portion of Dalmatia and various Adriatic Islands. This was not what had been agreed with Pavelić prior to the invasion; Italy had expected to annex all of Dalmatia as part of its irredentist claims.