This term corresponds to definiiton 1.
There are multiple definitions - click on the translation that matches your context.
if you sack someone then you dismiss them from their job
Members of the government have been trying to get him to sack his finance minister.
to pillage (=steal from, using violence) a town or a city, especially during times of war or conflict
The term vandals was the name originally given to the invaders who first sacked the city.