Until late 1940 Hitler hoped to establish peaceful German hegemony over the Balkans as part of his supply hinterland, but after the Soviet occupation of Bessarabia and northern Bukovina from Romania in late June, his hand was forced. On 7 October Germany invaded Romania to block the Soviet Army and to get access to the Ploiești oilfields. After Italy's disastrous invasion of Greece on 28 October the British intervened in accordance with the Anglo-Greek Mutual Aid Agreement, occupying Crete and establishing airfields within bombing distance of the Romanian oilfields. In late November Hungary and Romania signed the Tripartite Pact, joining the Axis powers and, although Yugoslavia initially refused to sign, Hitler now had control of the majority of the vast agricultural resources of the Great Hungarian Plain and Romanian oilfields.