1991 Sino-Soviet Border Agreement

Even as tensions lessened and leaders on both sides adopted more conciliatory attitudes, the border issue remained unresolved.

Despite their view of the previous border treaties as unequal ones, Chinese leaders were willing to negotiate on the basis of the modern boundaries.

The agreement largely finalized the 4,200 km (2,600 mi) border between the Soviet Union and China, except for a few disputed areas.

According to the estimates by Boris Tkachenko, a Russian historian, the treaty resulted in net territorial gain for China, which received about 720 km2, including some seven hundred islands.

Obviously, each country would receive a greater number of islands if the recognized main channel was closer to the opposite bank.

While the majority of the disputed territories lay in the west, the Russian Federation inherited only about 50 km (31 mi) of the former western Sino-Soviet border.

Specifically excluded from the agreement was the status of 5 km2 (1.9 sq mi) Abagaitu Islet, on the border between China's Inner Mongolia and Russia's Chita Oblast and near the cities of Zabaykalsk and Manzhouli.

After the invasion of Manchukuo during World War II, the Soviet Union unilaterally occupied many of the islands along the Amur River and prevented Chinese locals from entering.

These treaty conditions were subsequently reneged and the Manchu, Han, and Daur residents were deported, or massacred in pogroms Sixty-Four Villages East of the River The PRC relinquished claims to these lands during border negotiations.

Around 3 km2 (1.2 sq mi) of territory at Lake Khanka near the village of Tury Rog was transferred to Chinese control.

West of Lake Khanka lay a section of territory unilaterally seized from Manchukuo by the Soviet Union in 1933.

With the 1991 agreement, Russia transferred 9 km2 (3.5 sq mi) to China so that now the Sino-Russian border runs along the entire length of the river.

According to the agreement, 3 km2 (1.2 sq mi) of territory would be transferred to China, and Chinese ships would gain the right to navigate the Tumen river.

This portion of the agreement stirred up some controversy among some Russian officials from Primorsky Krai, as they felt that direct Chinese access to the Sea of Japan (through the Tumen River) would decrease the economic importance of Vladivostok and Nakhodka.

The Lake Khasan cemetery remained on the Russian side, and the Chinese officials underwent informal agreements to not build a port along the Tumen River.

The final position of the triangular border, where China, Russia, and North Korea meet, was successfully demarcated in 1998 after trilateral negotiations from all three countries, and went into effect in 1999.