Back then, the countries like Qing dynasty leased their land to the powerful nations which are capable to develop and cultivate a land. Japan had Manchuria, North East of China beyond Great Wall, a fatherland of Manchus, leased from Qing as a concession and the right for railroad.
The problem is this lease doesn’t come with the guarantee of safety, and it was more like the outlawed area and people and Manchu railroad were often assaulted by local bandits or those agitated by anti-Japanese fractions. Japanese referred to that problem as Manchuria and Mongolia problem, “Man-Moe” problem 満蒙問題.
You may think “then, why not give it up? it is out of Japan.“ But Japanese couldn’t. Because it was a special right given as a part of compensation after going through the interventions by Russua, Germany, and France, and finally got it after war Russo-Jpn war(Japan kicked Russia out of Manchuria) and 1st WW sacrificing all lives of Japanese soldiers.