Zhang became worried over Wu Peifu's growing military strength and anti-Japanese stance which threatened his backers in Japan. Using a financial crisis as a pretext, he removed Jin and replaced him with Liang Shiyi in December 1921. Wu forced Liang to resign after a month accusing him of being pro-Japanese. He exposed Liang's telegram ordering diplomats to back Japan on the Shandong Problem during the Washington Naval Conference. Zhang then formed an alliance with the Duan Qirui and Sun Yatsen. Both sides sent circular telegrams to rally their officers and denounce their enemies. On April 28, the First Zhili–Fengtian War began with Wu clashed with Zhang's army in Shanhaiguan and won a major victory forcing Zhang to retreat to Manchuria.