On 6 April 1941. German forces launched their invasion of Yugoslavia. Within a matter of days, Croatian separatists declared the founding of the Independent State of Croatia (Nezavisna Država Hrvatska, or NDH) under the leadership of Ante Pavelić.
On 17 April 1941, Croatia officially entered the war on the Axis side by declaring war on Britain.
To support their German allies, Croatian men began volunteering in large numbers to serve in Croatian units attached to the Wehrmacht, Kriegsmarine, and Luftwaffe.
During the period, the NDH issued a large variety of postage stamps. The entire collection can be seen here. There were, however, two sets of stamps commemorating the Croatian Legion. These are shown in this Croatian Legion section, in addition to in the NDH section of the website.