Actually from what we now know, NATO’s intention was to use the unprecedented sanctions to crush Russia’s economy, which they apparently expected would collapse within weeks. Ukraine’s job was to hold out the Russian advances for a few weeks until the collapsing economy forces Russia to retreat, and for the Russians come back to beg the US/EU to let them sell oil and gas again.

At the same time, we also know that Ukraine had been building up its military since 2014, with the explicit goal of recapturing Donbass and Crimea. If Ukrainian army had reached Donetsk city, it would have been a nightmare for the Russians to retake it again. The civilian casualties could easily go magnitudes of order higher. In this sense, Russia’s pre-emptive strike was almost inevitable if the goal was to prevent the Ukrainians from reaching Donetsk at all cost.