Serving as part of Vladimir Kappel's White army (nicknamed kappelevtsy), he was eventually appointed head of the Volga Cavalry Brigade in January 1919, and led this unit during several battles of the Eastern Front of the Russian Civil War.

[11] The war increasingly turned against the anti-Communist White movement, however, and Kappel's army was forced to retreat into Transbaikal during the Great Siberian Ice March.

One of the most powerful Chinese warlords was Zhang Zuolin, leader of the Fengtian clique and de facto ruler of Manchuria, where many of the White Russian ex-soldiers had settled down.

[24][4] Mercenary service was attractive for White émigrés due to the fact that many of them had problems finding stable employment, and the warlords at least offered a regular income.

In this conflict against Wu Peifu's Zhili clique, the Russians fought as part of the Fengtian foreign legion which also included 300 Japanese mercenaries and two Chinese companies.

In course of these operations, Nechaev and several other White Russian mercenaries were featured in the propaganda film Modern Warfare in China 1924–1925 which was produced by the Soviet Union.

[28] As the Soviet government was opportunistically supporting the anti-Left Fengtian clique at the time,[29] the White Russian general and his fellow anti-communist soldiers were portrayed favorably and sympathetically by the film's director, a Red Army colonel named Grinevskii.

[23] Zhang Zongchang served as Nechaev's direct superior for the following years,[32] and allowed the Russian lieutenant general to operate largely autonomous.

[34] By this time, the foreign legion already counted 800 officers, and 2,000 regular soldiers who had previously fought in the armies of Semyonov and Alexander Kolchak,[35] and four armoured trains.

[42][32] In November 1925, Leon Trotsky mentioned Nechaev in a speech to the Kislovodsk Soviet, claiming that he and his troops were paid by Great Britain to support Chinese monarchism.

[32] Soon after, the 65th Infantry Division suffered heavy casualties in another armed conflict with Sun Chuanfang, so that "only several hundred" Russians were left in the unit by 1927, when war erupted between the Fengtian clique and the National Revolutionary Army (NRA) of the Kuomintang.

Reduced in manpower, Nechaev and his forces mostly contributed to the Fengtian clique's resistance against the NRA's Northern Expedition by using their remaining armoured trains.

[42] In March 1927, the Chinese Communist Party (CCP) launched an armed uprising in Shanghai against the local warlord garrison of Zhang Zongchang and Sun Chuanfang,[44] who had allied himself with the Fengtian clique to resist the NRA.

[46] Nechaev's troops were among the 3,000 defenders of Shanghai's Zhabei district, and were only ousted from the city after heavy fighting with the CCP insurgents and NRA reinforcements.

[49][50] Nechaev's men still had at least three armoured trains under their control at the time, and initially assisted Zhang Zongchang in invading Manchuria to topple Xueliang.

After crossing the Luan River, however, Zhang Zongchang was trapped by the now-allied troops of the NRA and the "Young Marshal"; realizing that the position of their superior was lost, the White Russians defected and turned the guns of their trains on their former allies.

[15] Following the Sino-Soviet conflict, the Soviet authorities demanded that all White Russians had to be dismissed from both the Northeastern Army and the Chinese Eastern Railway, while their leaders,[52][53] among them Nechaev, were to be expelled from Manchuria.