He was active outside the Bulgarian occupied area of Macedonia, under the tolerance of the Italian and German authorities which used him in their fights with rival Greek EAM-ELAS and Yugoslav Communist resistance groups.

[5] At this time the Internal Macedonian Revolutionary Organization (IMRO) began sending armed combat groups (cheti) into Greek Macedonia and Thrace to assassinate officials and stir up the spirit of the oppressed population.

Kalchev came from a well known IMRO Bulgarian local family,[6][7] which emigrated from Greek Macedonia to Balchik, Bulgaria after the Second Balkan War.

As a consequence after the German invasion in Greece (6 April 1941) followed also a Bulgarian annexation of Eastern Macedonia and part of Western Thrace.

Bulgaria joined World War II siding with the Axis in an attempt to solve its own "national question" and fulfill the aim of "Greater Bulgaria", especially in the area of Macedonia (where much territory was lost in the Second Balkan War) and Western Thrace (former Bulgarian state international recognized territory lost to Greece in the Treaty of Neuilly).

A spontaneous and badly organized uprising around Drama, Greece in late September 1941 was violently crushed by the Bulgarian Army.

Bulgaria was interested in acquiring the zones under Italian and German occupation and hoped to sway the allegiance of the 80,000 Bulgarophones who lived there at the time.

[citation needed] In the first half of March 1943, Bulgarian military and police carried out the deportation of the majority of non-Bulgarian Jews, 13,341 in total, from the occupied territories, beyond the borders of Bulgaria before the war, and handed them over into German custody.

[citation needed] As recorded in the German Archives, Nazi Germany paid 7,144.317 leva for the deportation of 3,545 adults and 592 children destined for the Treblinka extermination camp.

[16] On March 20, 1943, Bulgarian military police, assisted by German soldiers, took Jews from Komotini and Kavala off the passenger steamship Karageorge, massacred them, and sank the vessel.

The appearance of Greek partisans in Western Macedonia persuaded the Italian and German authorities to allow the formation of Slav security battalions led by Bulgarian officers.

Kalchev's active collaboration with the Italian and German Army in fighting the resistance forces and the using of local conscripted manpower born a very unpleasant situation for this pro-Bulgarian Slavophone part of the population after the end of the war, leading to a new wave of emigration to Bulgaria and Yugoslavia, the last (since World War I) members of the Bulgarian minority of Greece.