Kazakhstan is isolated from the world’s oceans, but borders the Caspian Sea on its west. The Soviet Union completed the Volga-Don Canal in 1952 to allow shipping between the Caspian Sea and the Sea of Azov, the northeastern arm of the Black Sea that connects through the Kerch Strait, across which Russia built a recently damaged bridge to occupied Crimea. From there, Kazakhstani ships can reach the Mediterranean.
Russia has recently granted Kazakhstan permission to use the Volga-Don Canal for its commercial ships, which will be carrying mainly Chinese goods. Those two countries now have an interest in keeping the Black Sea and the Kerch Strait open.
A shorter route has been proposed (red line on map), but it’s not clear when that could be built.
Sergei Prokofiev wrote the tone poem The Meeting of the Volga and the Don to celebrate its completion. The Wikipedia article is worth reading.
Cross-posted to Nuclear Diner