Во многих странах это день траура,

Во многих странах это день траура, потому что во время Великой Отечественной войны эти страны атаковали и устраивали концлагеря.

Results (English) 1:

In many countries, this day of mourning, because during the great patriotic war these countries attacked and made camp.

Results (English) 2:

In many countries, it is a day of mourning, because during WWII, these countries attacked the camp and arranged.

Results (English) 3:

in many countries, this is the day of mourning, because during the great patriotic war, those countries and had attacked the camp.