'Strafe' was a German unrealised plan for an invasion of Bulgaria if that country could not be persuaded to become a willing ally in the Tripartite Pact (1941).
The government of Bulgaria, led by Georgi Kyoseivanov, the prime minister, declared neutrality on the outbreak of World War II, and while it was determined to maintain this until the end of the war it nonetheless hoped for bloodless territorial gains in order to recover the territories the kingdom had lost in the 2nd Balkan War (1913) and World War I (1914/18), as well as gain other lands with a significant population of ethnic Bulgarians but occupied by neighbouring countries. However, it was clear that the central location of Bulgaria in the Balkans would inevitably attract strong external pressure by both sides in World War II, though the country had a non-aggression pact with Turkey. On 7 September 1940, Bulgaria succeeded in negotiating the recovery of Southern Dobruja from Romania, which had held the area since 1913, in the Axis-sponsored Treaty of Craiova, and this recovery reinforced Bulgarian hopes for resolving other territorial problems without direct involvement in the war.
After the failure of Italy’s 'Emergenza G' invasion of Greece in October 1940, Germany demanded that Bulgaria join the Tripartite Pact and permit German forces to pass through Bulgaria to attack Greece in order to help Italy. While the Bulgarian government was reluctant to get involved in the war, the threat of a German invasion, as well as the promise of Greek territories, led Bulgaria to sign the Tripartite Pact on 1 March 1941 and thereby join the Axis bloc, and as the USSR currently had a non-aggression pact with Germany there was little popular opposition to this decision.