Ukrainian forces are advancing on the northeastern city of Kharkiv, pushing an already thin Russian military back on its heels and putting additional stress on the invaders, who have already experienced a significant reduction of combat readiness due to sustained losses, the Wall Street Journal reports.

The offensive targets Russian supply routes into the currently occupied eastern and southern parts of Ukraine, key industrial and shipping regions of the country.  The Ukrainians are succeeding on the battlefield thanks to arms coming from allies like the United States and European Union nations.  Comparatively, Russia has purchased munitions from North Korea and drones from Iran as its internal military suppliers are unable to keep up with the needs on the battlefield.

Russia’s losses have been far greater than the Kremlin calculated, with estimates of personnel casualties ranging from 15,000 to 50,000 dead.  US intelligence estimates put casualties–those killed, wounded, injured, captured, or missing–at 80,000 during an August assessment. 

Russians invasion of Ukraine, started in February with an expectation that they would overrun the nation within weeks, was planned to take advantage of typically mild weather in the region over the spring and summer.  However, as autumn and winter approach, Russia now has to prepare for severe weather.  Russia started its offense in the east by bombarding urban centers with artillery, missiles and rockets, satisfied with destroying the cities before occupying them.

However, with Russia’s supplies and reinforcements stretched, the invasion has stalled and regressed in certain areas in the east.   Russia is reliant on “contract” soldiers–men who have voluntarily entered military service–to fight on the front lines, but with high casualty rates, its manpower is thinning and they’re having difficulty recruiting conscripts to enter the fight.

Ukraine’s goal is likely to capture Kharkiv, Ukraine’s second largest city and the regional governmental center, before winter sets in to form a defensive position and a forward location for future operations.