In 1645 Friedrich began his military career in the Swedish Army in Poland and took part in the siege of Copenhagen in 1660.

Originally, he had planned to return to Germany but when he visited the Danish court, King Fredrick III offered him a position as head of the new cavalry lifeguards.

In February 1678, Arensdorff became commander-in-chief of the Danish army in Scania, a position he was most reluctant to accept, but the king insisted.

[12] In the summer of that year, the Danish main army set out to lift the Swedish siege on Kristianstad.

King Christian was keen to face the Swedes in another field battle, Arensdorff was reluctant and the rest of the war council was uncertain.

In the end, the Danes gave up the whole enterprise and left the commander of Kristianstad, Carl Heinrich von der Osten, to negotiate honourable terms.

[13] During this disastrous summer campaign, Arensdorff signed orders to both regular officers and irregular friskytter captains to torch and destroy several cities and castles in Scania.

At the first stage, Arensdorf was condemned to lose his honour, property and life but after the Scanian War, he was reprieved by the King.[16].