Whakaotihia te rerenga e whai ake nei: Ko Aarnio he kaihauturu me nga White Guards i te Savonia Front i te Pakanga a Finnish Civil. I muri mai ka uru ia ki te Pakanga Independence o Estonia, te Pakanga Independence o Latvia me te
Ko te haerenga o te matua keke ki te Rāwhiti o Karelia. I whakawhitihia a Aarnio mai i te mahi hōia ki te ope hoia i te tau 1920. I puta ia i te Kadettikoulu i te 1926 me te Sotakorkeakoulu i te 1933. I whakatairangahia a Aarnio hei rangatira i te 1929 ka mahi i te tari hononga o waho o te General Staff.