Qing dynasty leased their land to the powerful nations which are capable to develop and cultivate it. Manchuria is in North East of China beyond Great Wall, a fatherland of Manchus, and Japan got a concession in Manchuria leased by Qing and the right to own the southern railroad taken over from Russia by Treaty of Manchuria (満洲善後条約) in 1905 (See Japan never invaded in a modern era) .
After Xinhai revolution in 1911, Japan was in a trouble since the owner of concession in Manchuria, Qing dynasty, lost a power. Japan had to renew the treaty with a new leader of Han Chinese government, Yuan Shikai, the treaty of 21 demands. Yet he died soon In 1916 and the only hope Sun Yat-sen also died. China was at disorder and in civil war where multiple Han Chinese warlords claimed “China” including Manchuria.
This page shows more specifically what rights and treaties Japan had and how they were violated by Han Chinese, and also shows all other troubles, which are generally referred to as Manchuria and Mongolia disorder state problem (Man mou mon dai 満蒙問題). You may think “then, why not give it up? Manchuria is out of Japan.“ But Japanese couldn’t. Because it was a special right Japan finally acquired after going through costly Russo-Japanese war.
The historical documents written at that time in 1932 below explain in details. In this section, since many of contents are redundant, their summaries are shown.
Iron-Blooded Resolution? : The Truth Behind the China-Japan Pending Issues 鉄血解決? : 対支懸案の真相
Japanese Official document (almost the same as above)
Army Ministry Pamphlets (9 volumes) 1931, 陸軍省パンフレット９冊 昭和６年
Multiple Han Chinese leaders claimed Manchuria and harrassing Japanese property with a tax or agitating people into anti-Japanese.
Passengers on railroad were often terrorized by local bandits or those agitated by anti-Japanese fractions.