Consolidating Youzhou In 299, during
Empress Jia's rule behind the curtains, she had the Crown Prince,
Sima Yu, under house arrest in Xuchang. The following year, Wang Jun and the eunuch Sun Lü (孫慮) assisted her in poisoning Sima Yu. Wang Jun received the title General Who Pacifies The North and Imperial Inspector of
Qingzhou. After a while, the court moved him to General Who Calms The Northern Frontiers and Chief Controller of Youzhou. While in Youzhou, Wang Jun sensed that civil war would soon ensue in northern China. Thus, he began initiating alliances with the neighbouring barbarian tribes to secure his position. He married his two daughters; one to the chieftain of the
Xianbei Duan tribe,
Duan Wuwuchen and another to a general of the Xianbei
Yuwen tribe, Sunuyan (素怒延). In 301,
Emperor Hui of Jin's regent,
Sima Lun, deposed Hui and declared himself emperor. The three princes, Sima Ying,
Sima Yong and
Sima Jiong, promptly began an alliance to restore Emperor Hui. Wang Jun remained neutral throughout the war and refused the send out his troops. He even confiscated letters from the coalition calling to arms in Youzhou to prevent anyone from joining them. Sima Ying was particularly frustrated at Wang Jun's actions and considered attacking him but decided not to due to more pressing issues. After overthrowing Sima Lun, Wang Jun received the office of General Who Secures the North.
War with Sima Ying In 304, Sima Ying and Sima Yong became Jin's paramount leaders after killing the Prince of Changsha,
Sima Ai. While in power, Sima Ying sought to eliminate Wang Jun, still begrudging him for his conduct in 301. Wang Jun himself was also not pleased with the outcome of Sima Ying and Sima Ai's war. Sima Ying appointed his trusted subordinate, He Yan (和演), as Inspector of Youzhou with orders to assassinate Wang Jun. He Yan colluded with the
Wuhuan Chanyu, Shen Deng (審登), and when the two travelled with Wang Jun to Qingquan (清泉; south of present-day
Beijing), they agreed to have him killed there. However, a heavy storm drenched their troops' equipment and foiled their plans on the day of their attempt. Shen Deng perceived the storm as a sign that the Heavens favoured Wang Jun, so he defected to Wang Jun and revealed the plot. In response, Wang Jun and Shen Deng besieged He Yan and forced him to surrender. After executing He Yan, Wang Jun assumed total control over Youzhou. Sima Ying tried summoning Wang Jun to court, but Wang Jun camped at
Jizhou instead. Wang Jun brought along Duan Wuwuchen and a Wuhuan chieftain, Jiezhu (羯朱), and allied with the Inspector of
Bingzhou,
Sima Teng. They defeated Sima Ying's general, Wang Bin (王斌), and as they approached Sima Ying's base in
Yecheng, Wang Jun's vanguard general,
Qi Hong, also defeated
Shi Chao. Sima Ying panicked and fled to
Luoyang, allowing Wang Jun to occupy his city. The Xianbei had Yecheng sacked and abducted many women from the city. After Wang Jun returned to Jicheng, he executed many of the Xianbei soldiers who partook in the abductions, and around 8,000 bodies reportedly filled the Yi River (易水; in present-day
Yi County,
Hebei).
Sima Yue's coalition In 305, Wang Jun was one of the many governors east of Luoyang to acclaim the Prince of Donghai,
Sima Yue, as coalition leader to overthrow Sima Yong and bring Emperor Hui back to Luoyang from
Chang'an. Wang Jun lent his Xianbei troops to the Prince of Fanyang,
Sima Xiao (司馬虓), which proved vital to defeating Sima Yong's powerful ally,
Liu Qiao. Wang Jun later had Qi Hong lead his elite Xianbei and Wuhuan charging cavalry to serve in Sima Yue's vanguard. In June 306, Qi Hong and others entered Chang'an, and Wang Jun's Xianbei troops sacked the city, leaving 20,000 dead in their wake. After Emperor Hui returned to Luoyang, Wang Jun became Grand General of Agile Cavalry, Commander over the eastern tribes and the military affairs of Hebei, and acting Inspector of Youzhou for his contributions. The court also merged the state of
Yan into Wang Jun's fief. In 307,
Emperor Huai of Jin ascended the throne. He appointed Wang Jun Minister of Works and Protector of the Wuhuan. ==Conflicts with Shi Le and Liu Kun==