 He took part in the preparation for a war against Muscovy in 1579 – 1581 , where he contributed a group of 400 or 600 mercenaries . Through he had little prior military background nor experience , he was interested in mastering the military art , and proved to be an adept learner . With Batory 's support , he begun filling in for some of the roles of Grand Crown Hetman Mikołaj Mielecki , particularly when Mielecki was not present . While not campaigning , he was also instrumental in ensuring that the ongoing political support for the war . In 1580 he was hit by another personal tragedy , as his wife died in labor , together with their child ; entering a short period of depression . 
