Yan invested in Shanxi's industrial infrastructure, and by 1949 the area around Taiyuan was a major national producer of coal, iron, chemicals, and munitions. Yan was able to protect the province from his rivals for the period of his rule partially due to his building of an arsenal in Taiyuan that, for the entire period of his administration, remained the only center in China capable of producing field artillery. Yan's army was successful in eradicating banditry in Shanxi, allowing him to maintain a relatively high level of public order and security.