Nazi Germany launched a two-pronged invasion in April 1941, executing Operation 25 against the Kingdom of Yugoslavia and Operation Marita against Greece. The military actions stemmed from a need to secure strategic positions in the Balkans after the region had become increasingly unstable. Following the coup in Yugoslavia in March 1941 that overthrew the pro-Axis government, Adolf Hitler viewed the new Yugoslav government as a threat to Axis interests. The invasion began with aerial bombardments and swiftly followed by ground attacks, which overwhelmed the Yugoslav forces within days, leading to the country’s rapid capitulation.

Simultaneously, Operation Marita aimed at Greece, which had already been engaged in war with Italy, and was now facing a larger German offensive. Notably, British Commonwealth forces attempted to support Greece, but their efforts were undermined by the strength of the German Blitzkrieg tactics. German forces advanced through Thessaloniki and rapidly pushed southward, leading to the occupation of Athens by the end of April. The swift success showcased the effectiveness of German strategies and military technology, solidifying their control over the region and ensuring the Axis foothold in South-Eastern Europe.

The operations ultimately altered the dynamics of warfare in the Balkans, with extensive repercussions for both Yugoslavia's and Greece’s territories. The effectiveness of the blitzkrieg strategy during these operations highlighted the weaknesses in the Allied response and established a pattern that would be seen throughout the conflict. This marked a significant phase in the expansion of Nazi Germany's influence in Europe during World War II, leading to further territorial gains.