The correct answer is - China was too weak to prevent other nations from controlling parts of its territory.
In the late 1800's, China was in a terrible situation. The Manchu were ruling over the country in a terrible way, and also they were very corrupt, so they didn't even put an effort to stop the European countries to take over parts of China.
Multiple European countries were able with relative ease to take over the most important and biggest ports of China, as well as the area surrounding them, and they did that because of the great strategic position, economic reasons, and political reasons. It was obvious, that if the European countries had decided to take parts of China by force and divided the country into multiple parts it was very possible, so the concern was real and on place.