In 1968, the Soviet Federation assembled 75 divisions and tens of thousands of tanks, so why did it not cross the Yalu River? In the 60s of the last century, Sino-Soviet relations were in danger of collapsing. The Soviet side first withdrew all technical specialists in China, canceling all assistance programs.
In addition, China is required to repay all loans in the short term. China did not give in and gathered all its strength to pay off the Soviet Union's loans. By 1968, Sino-Soviet relations had developed into a state of confrontation and were in danger of war. The Soviets amassed a large number of forces in the Far East, but in the end they were not able to cross the Yalu River. Peace can be maintained only if each side takes a step back. At that time, it seemed that the Soviet Federation was already preparing for war. According to data, the Soviet Union amassed more than a million troops in the Far East at that time, including 20 divisions on the northeastern border, with 400,000 troops, and 55 divisions and regiments on the Mongolian border and in the Far East, with more than 700,000 troops. With regard to armament, the Soviet Federation assembled nearly 5,000 fighters, 3,500 anti-aircraft missiles, and tens of thousands of tanks and armored vehicles. Even international public opinion at that time believed that the Soviet Union was going to have one.
Eventually, however, in 1969, the Soviet Federation repeatedly carried out armed incursions against the Chinese island of Treasure, which is located in the center of the main route of the Ussuri River in Heilongjiang Province.
First of all, the state of the Cold War at that time was unfavorable to the Soviet Union. In the 70s of the last century, the United States developed rapidly in all aspects, and the pressure on the USSR became more and more serious. If the Soviet Union had amassed heavy forces, it would have been unable to move in the Far East, and the Soviet Union would have lost its homeland to the United States and its allies in Europe. This was a real problem in the USSR. China and the Soviet Union had a naturally close relationship, and although the two sides had differences, they were far from being resolved by war, which was a disguised weakening of the Soviet Union's own power.
Secondly, China was fully prepared, and the USSR did not have the confidence to defeat China in one go.
At that time, China had an army of more than 5 million people. In terms of defense, China carried out large-scale third-line construction very early, moved key industries to the mountains in the west, and set up several defensive positions in the north. China has atomic and hydrogen bombs. This was a powerful deterrent that the USSR had to take into account. The Far East was far from the center of the Soviet Union, with inconvenient transportation and difficult supplies. If there is a tug-of-war with China, I am afraid that the Soviet Union will collapse in its entirety. Modern history has also proved that no foreign invader has been able to completely defeat China.