Final answer:
The region in northeast China handed over to Russia via 1858 and 1860 treaties is Manchuria. This strategic and industrially significant region fell under Russian control through the Treaty of Aigun and the Convention of Beijing during a time of Qing dynasty weakness.
Step-by-step explanation:
The northeast Chinese region handed over to Russia in treaties in 1858 and 1860 is D) Manchuria.
Manchuria, home to the Manchu people, has been an area of significant historical and geopolitical activity. Russia's expansion and the strategic value of Manchuria led to the treaties that transferred its control. The Treaty of Aigun in 1858 and the Convention of Beijing in 1860 formalized this transfer, constituting a significant change in the territorial arrangements of the time.
During this period, the Qing dynasty was forced to cede territories under pressure from various foreign powers, including Russia. Manchuria later played an essential role during the Japanese occupation in the early 20th century when it was transformed into the puppet state of Manchukuo before ultimately returning to Chinese control post-World War II.