A territorial dispute deriving from nineteenth-century treaties imposed on China by an ascendant Russia became an integral element of the falling-out between the two great communist powers, the USSR and the People's Republic of China, in the second half of the twentieth century. That dispute, which came to be concentrated on the issue of the exact boundary alignment within the Amur and Ussuri Rivers, was made more intractable by the ideological estrangement between Moscow and Beijing. The dispute, in turn, fed back to embitter that estrangement. Contradictory interpretations of the nineteenth-century treaties taken by the two sides were compounded by their different approaches to the problem of boundary settlement: Beijing sought settlement on the basis of compromise, but insisted that could be achieved only through full renegotiation. Moscow read into Beijing's approach covert irredentism, refused to negotiate, and exerted military force to impose its own interpretation of the treaties. China resisted, meeting force with force, and in the 1969 clashes on the Ussuri River prevailed, bringing the conflict to the brink of all-out war. In 1986 Moscow broke a protracted deadlock by reversing its approach and agreeing to negotiate. By 2005 the full extent of the Sino-Russian boundary had been agreed and legitimized in new treaties.