What? Russia DID push into China, when it was able to. Russia didn't have any appreciable military edge over China until the 19th century and so the border remained fixed according to the line demarcated by the treaty of nerchinsk. That treaty was originally signed after China defeated Russia in border conflicts.

In 1858, after China had already suffered invasion and civil war, Russia took outer manchuria in the treaty of aigun, in the middle of another opium war and the taiping rebellion. The goal of this was to establish a pacific port, aka Vladivostok. Russia then connected this region with a railway running through Manchuria, so China was again forced to cede partial sovereignty so that russia might build and administer the Manchurian railway. A brief war erupted over this issue in 1929.

The USSR created a communist government for outer Mongolia which became de facto independent. Independent Mongolia was recognized by the PRC but remains unrecognized by the ROC.

In Xinjiang soviet forces entered China in 1934 in support a soviet-friendly warlord named Sheng Shicai. The USSR continued to intervene and seek influence in Xinjiang for several years, until they were kicked out by their client warlord during WW2, after which they never attempted to regain control.

I'm not sure how any basic overview of sino-russian history could have skipped over any of this.

You are missing something. Russia did push into China, repeatedly.

In 1689, Russia signed the Treaty of Nerchinsk with China. This was the first treaty signed by a Western nation with China, and it did a few things. It set the border between the two countries and forced Russia out of the Amur River basin. It stopped Russian expansion eastward at the cost of ceding control of land east of Lake Baikal to Russia. It also allowed Russia trade access to China.

This was a big deal, because Russia had been sending traders and freebooters eastward for more than a century by this point. The first recorded transit of the Bering Strait took place more than 40 years before the treaty, and Russians and their client people were beginning to conflict with the Chinese.

Trade access was even more important. Russian furs were valued in China, and Chinese goods were valued in Europe. Access to China was difficult, which made its trade goods worth a great deal. As the middleman in the Chinese-European trade, Russia benefited.

By the 19th century, things were changing. The Opium Wars and the Taiping Rebellion weakened China, and Russia was growing stronger and more capable. By the middle of the century, it had recovered from the Napoleonic invasions and was again looking eastward. The Amur River valley, off limits under the Treaty of Nerchinsk, was subject to larger and larger incursions by Russian agents.

With the Russians threatening to enter a war of expansion against China, Qing representatives agreed to a treaty with Russia in 1858 and another in 1860 that turned over the Amur region and what is sometimes called Outer Manchuria. Think of the location of Vladivostok. That port was founded by Russia after the Treaty of Peking in 1860.

Forty years later, Russia expanded at China's expense again. During the Boxer Rebellion, Russian forces invaded China, in part to safeguard Russian railroads in Manchuria and in part to assist the foreign legations besieged in Peking. Official orders stated that Chinese territory was not to be annexed, but Russian authorities still had control of much of Manchuria as late as 1905, when the Japanese enlisted Chinese locals as guerrillas behind the front lines of the Russo-Japanese War.

Russia made significant incursions into Manchuria in the late 1890's and again immediately following World War 2 in moving into what was previously Japanese held territory.

To assume that the Russians were significantly superior to China from a military standpoint during the late nineteenth century has to be considered in relation to the other nations occupying large concessions in China at the time, the logistics (distance), and the early 20th century Russian naval defeat at the hands of Japan indicating Russia was militarily less able than some might believe.

After World War 2 while Russia did occupy areas of what is now China their focus was westward given the recent devastating war with Germany and the jockeying for position with the Western powers in Europe. By the time things had solidified in the west China had developed increased military ability and ultimately had atomic capabilities to counter any moves into their territory. On top of all that Russia and China represented the two largest communist countries in the world at the time and cooperated to varying degrees in the Korean and Vietnam conflicts.

As Wereflea's response indicated Russia's interests in China have been mostly economic and not territorial. Those interests largely focused on Manchuria.

Eehh...calling Russian rule over Finland from 1809 to 1917 as subjugation is a bit of an overstatement.

We had it pretty easy in here. Alexander II liked Finland, and we liked him. Alexander III didn't have a beef with Finns and we didn't have one with him.

It was Nikolai II who was a sonofabitch towards Finland, so we assassinated our Governor-General Bobrikov, and helped Lenin out a couple of times. That turned out pretty well, didn't it?

Talking about Finland in WW2 in terms of being subjugated by Russians is...well, I guess you can call it subjugation if you're drowning your enemy in the corpses of your soldiers..

Calling the Soviet era policy towards Finland after the war as subjugation would be even more of an overstatement.

We had it even more easier than we had it when we were a Grand Duchy of Russia.