An interesting dynamic has emerged in the last 10 days or so. Whereas there was widespread anticipation that Aleksandr Lukashenko was about to order the deployment of Belarusian troops to assist in the invasion Ukraine, and threaten the western part of the country and to assist in a final assault on Kyiv, this has not happened, and it likely will not happen (https://www.cnn.com/2022/03/22/europe/belarus-ukraine/index.html). There are three reasons for this.
First, there is the changing situation on the ground. Russia has clearly withdrawn forces around Kyiv with the intention of redeploying them Eastward to seize the Donbas and Mariupol (if not the entirety of Eastern Ukraine up to the Dniepr River). The redefinition of the goals for the war has significantly reduced the need for Belarus to join the war from the Russian perspective. This makes it easier for Lukashenko to stay out of the war, which according so some observers is what Lukashenko prefers.
Second, it is not surprising for Belarus to be somewhat reluctant to go “all in” to support the Russian war effort. It is one thing to offer bases for Russian troops, it is entirely another thing to deploy your own troops across the border. Given the massive protests of two years ago that almost toppled the regime, It would seem that Lukashenko would prefer keeping the best of his military at home to protect the regime, not to die on Ukrainian battlefields.
Third, it was not too long ago that Lukashenko tried to cultivate good relations with Ukraine, and to chart a genuinely neutral position (and even taking some pro Ukrainian positions in some areas such as defense cooperation) after Russia’s annexation of Crimea in 2014 (https://www.theguardian.com/world/2014/aug/26/belarusia-president-lukashenko-benefit-host-ukraine-russia-talks). Lukashenko, prior to the protests that almost overthrew his regime, also remained open to overtures from the west despite his close ties to Russia.
I don’t think that Lukashenko wants to be seen as a slavish devotee to the Russian war effort. Thus, despite widespread warnings that Belarus would join the war in a matter of days, this did not happen and I do not expect to happen now. This might make Belarus an important player in negotiating a settlement to end the war, especially if Lukashenko seeks to back away from the image that he is merely a puppet of Vladimir Putin- especially as the Russian war effort sputters.