Russian forces continue to make small but rapid gains outside of the eastern Ukrainian city of Avdiivka, attributable in part to dwindling Ukrainian ammunition and declining Western aid.

But there’s another reason the Kremlin’s troops are advancing in the area: poor Ukrainian defenses.

Ukrainian officials may have been too focused on offensive operations last year to dedicate the necessary resources to building the kind of multiple trenches and tank traps that Russian engineers built since late 2022 in the country’s south, the U.S. officials and military experts said.

There may have also been a psychological element at play, the U.S. officials said. If Ukrainian troops heavily mined certain areas to thwart Russian advances, it would be a tacit acknowledgement that they were unlikely to carry out offensive operations in the same area at a future date. They’d effectively be writing off that territory to the Russian military, the officials said.