The Amur Host was based in the Amur province (also known as the Priamur at the time), and their primary role was patrolling the border along that river up to Khabarovsk. Their main centre was Blagoveshchensk.
The Amur Host soldiers wore standard Cossack dress, with their distinguishing colours being yellow and green.
The Amur region was centre of support for the revolution throughout the Civil War, and large numbers of Reds fell back there from the TransBaikal and Primorye (Maritime) areas in 1918 as the counter-revolution grew stronger. With no large towns and terrain that was easy to hide in, they were in little danger of being eradicated by the small White forces available. The distance from Moscow meant that these partisan forces were not under strict control, which meant they were as likely to be Anarchist or SR as purely Bolshevik.
The Amur Cossacks themselves failed to organise much resistance to the Soviets. Instead the area more or less around the rail line was cleared by Semënov and the Czechs, who then controlled it until the Soviets arrived. The Amur Host formally subordinated itself to Semënov, but in practice the area was lawless, with petty warlords coming and going.
There was never much of a Host army, more some self-defence units. Active campaigning was done largely by outsiders.
At the start of 1920 the local Ataman called his Cossacks together to ask if they would support the Whites. When it was clear that they would not, he decamped, and the area was more or less entirely in partisan hands.
A few Amur Cossacks fled to the Primorye region, and joined up with White forces there. They grew to three small sotnias, one on foot, so that in 1921 it they became the Amur Cossack Divizion.