After the outbreak of World War II, the Bulgarian government pursued a policy of non-alignment. In the fall of 1940 it rejected plans for a combined Italian-Bulgarian attack against Greece. And when Italy alone invaded Greece, Bulgaria facilitated Greek resistance by her own passivity. When Germany called on Bulgaria to enter the Tripartite Pact and make its territory available for a German attack against Greece, the Bulgarian leadership succeeded in retarding the talks. At the same time, the Soviet Union, Germany's Balkan rival, tried to entice Bulgaria into concluding a pact of mutual assistance by offering the whole of western and eastern Thrace at the expense of both Turkey and Greece. Bulgaria refused, and on 1 March 1941 joined the alliance with Germany in hope of territorial gains. It took this step only when it seemed unavoidable.