Russia and Belarus will seek to further grow the threat to Ukraine's northern border in the coming weeks, but a Russian ground invasion from Belarus or Belarusian forces joining the war remains unlikely because of Belarus's own calculations. A surge of military activity in Belarus over the past week is fueling fears in neighboring Ukraine that Russia is preparing to launch a renewed thrust toward Kyiv — potentially with the help of Belarusian forces. The week began with Belarusian President Alexander Lukashenko's Oct. 10 announcement that he had agreed to deploy a joint contingent of Russian and Belarusian forces in response to alleged threats from Ukraine. On Oct. 14, Lukashenko then announced the introduction of a ''counter-terrorist operation regime'' — the implications of which are unclear — and that the deployment of the new Russia-Belarus joint force group, including to his country's southern borders, was connected to an ''elevated terrorist threat'' and alleged ''aggravations'' from NATO and Ukrainian forces. On Oct. 15, the Belarusian defense ministry said the first Russian soldiers who will take part in the new joint force had arrived in the country, and on Oct. 16 claimed that nearly 9,000 Russian soldiers would be deployed to Belarus as part of the new regional grouping of Russian and Belarusian troops in accordance with the two countries' alliance, known as the Union State alliance. The deployment and other factors — such as rumors that Belarus is conducting a military mobilization — have raised concerns that Russia is readying to launch another offensive against Kyiv after failing to seize the Ukrainian capital earlier this year, and that Belarus is also readying to effectively join the war on Russia's side.

On Oct. 13, the Belarusian opposition newspaper Nasha Nivathat reported that Lukashenko had decided to conduct a ''covert mobilization'' under the guise of checking military fitness and summoning conscripts among rural Belarusians, citing unnamed sources in the president's administration. The report came a day after Belarus's parliament approved legal changes canceling military draft deferments for students abroad who were not sent to foreign education institutions by the state.

Russian forces' buildup in Belarus is likely intended to draw some Ukrainian military resources from the south to the north, free up Russia's own training grounds, and use the threat of an invasion from the north to gain leverage during potential peace negotiations with Kyiv. On Oct. 14, Russian President Vladimir Putin griped that the negotiation process with Ukraine had stopped immediately after Russian troops withdrew from northern Ukraine at the end of March. If Putin believes that Russia's retreat from Kyiv earlier this year prompted Ukraine to abandon peace talks, he may also believe that weakening Ukraine's position and forcing it back to the negotiating table can be best achieved in the near-to-medium term by threatening Ukraine's capital again — or at least cultivating this perception in order to make the threat appear more plausible in coming weeks. For Moscow, a higher number of Russian troops in Belarus or the possibility of Belarus joining the invasion helps maintain the threat of an assault on Kyiv. Additionally, Russia likely views Belarus as a preferred location to train its newly drafted Russian reservists (and, in turn, reduce and prevent overcrowding at its own bases and training grounds) amid Moscow's ongoing military mobilization. To that end, the joint contingent and Belarus's threatening actions could force Kyiv to deploy some of its reserves toward Belarus rather than along the front in southern Ukraine. Such a diversion of Ukrainian resources, so Moscow hopes, may help Russian forces stop Ukrainian advances and seize the initiative in the south, as Russia's newly mobilized troops eventually reach the front in the coming weeks and months.

During the G-7 summit on Oct. 11, Ukrainian President Volodymyr Zelensky proposed deploying a mission of peacekeepers on his country's northern border to rule out possible provocations against Ukraine from Russian or Belarusian forces in Belarus.

Belarus, for its part, is agreeing to increase the threat to northern Ukraine in exchange for Russian economic support. While Belarus has supported Russia since the start of the war, Ukraine never perceived Minsk's role in the conflict as a serious threat. But Belarus's recent activity suggests it's trying to change that assumption, as Minsk tries to increase its support for Russia and obtain additional political and economic concessions without intervening directly in the conflict. In fact, the deployment of the Russian-Belarusian joint force group to the Ukrainian border came after Lukashenko and Putin met in Sochi on Sept. 26-27 to discuss deepening their countries' economic, security and political cooperation. During those meetings, Lukashenko likely received Putin's preliminary approval for the $1.5 billion ''import replacement'' loan from Russia that Minsk announced it had secured on Oct. 7 — just days before the announcement of Russia's new troop deployment to Belarus. This indicates that Lukashenko is increasing the perceived threat of his forces joining the war against Ukraine in exchange for additional financial support from Russia to prop up Belarus's heavily sanctioned economy. But for such an arrangement to be worth its cost for Russia, Minsk must follow Moscow's instruction to maintain the credibility of that threat, hence the surge in military activity immediately following the loan's announcement.

On Oct. 9, videos from Belarusian media showed 28 Ural trucks and 8 T-72 tanks moving from Belarus to Russia, which analysts later determined were destined for eastern Ukraine. The incident was the latest example of Russia removing materials from Belarusian stockpiles, and strongly suggests Belarus is not preparing to actually join the fight in Ukraine, as moving precious equipment out of the country is not a rational action for a nation preparing to go to war.

On Sept. 16, as part of the two states' further integration within the Union State, Russia and Belarus signed a draft agreement on a general harmonization on the collection of the value-added tax and excise duties. The move was widely interpreted as giving Russia control over Belarus's tax customs policies and underscores Minsk's increasing reliance on Moscow.

Russia is unlikely to quickly accumulate enough forces to launch a successful attack against Kyiv, which will reduce the immediate risk of a renewed Russian thrust into northern Ukraine through Belarus. According to NATO estimates, at least 30,000 Russian troops — including many of Russia's most elite units — took part in Russia's attempt to seize the Ukrainian capital in the early stages of the war, which failed despite Kyiv being relatively undefended, as most of Ukraine's equipment and experienced soldiers were concentrated in the country's east at the time. The Russian forces now arriving in Belarus, by contrast, appear to be largely composed of newly mobilized Russian forces, and they are arriving at Belarusian training grounds largely bereft of heavy equipment. On Oct. 14, Lukashenko also said that ''demanding 10,000-15,000 soldiers from Russia'' was not necessary at this time — suggesting that Russia may begin with a relatively small deployment of roughly that size, even if it becomes larger in the coming months. In addition, Ukraine's forces are currently better equipped and fortified than they were when Russia first tried to take Kyiv, which further indicates the current Russian troops in Belarus are unlikely to succeed where their predecessors failed. In fact, the number of Russian forces needed to realize another attack on the Ukrainian capital would be much better used in the more favorable terrain of southeastern Ukraine than the swampy marshes between Kyiv and Belarus. Moreover, while Russia will still seek to grow the threat of an attack on Kyiv in the coming weeks and months with many more forces and equipment, Ukraine and the West will likely have ample warning to prepare and neutralize this threat.

Belarus remains unlikely to join the war because its forces cannot guarantee a Russian victory, while their participation would destabilize Belarus and leave Lukashenko without leverage vis-a-vis Moscow. The Belarusian armed forces total just around 48,000 combat personnel and are poorly equipped and inexperienced. This force is widely believed incapable of altering the trajectory of the war by successfully attacking Ukraine alongside Russian forces — even if Belarus conducts mobilization to bring tens of thousands of poorly motivated additional soldiers into the war. Lukashenko would likely only consider joining the war if he believed his forces could actually ensure a decisive Russian victory and force Kyiv to accept the loss of its territory, and, ideally, prompt some sort of pro-Russian regime change in Kyiv. But Lukashenko likely does not believe his forces could accomplish this, and it is unclear what Putin could offer to convince Lukashenko to bring Belarusian troops into the war. Coercion of Lukashenko — by, for example, withholding economic support or forcing Belarus into the war — would likely only further destabilize Lukashenko's regime, and make keeping Belarus in Moscow's orbit more politically tenuous and expensive. Lukashenko is only likely to bring his country into the war if he believes it's necessary to preserve his own regime (and, by extension, Putin's) and ensure a Russian victory, but both of these conditions are currently unsatisfied and will likely remain so. Therefore, Minsk and Moscow are likely to engage in provocative military deployments and maneuvers in Belarus and possibly even false-flag attacks on its own soil to increase the perceived threat, but Belarus remains unlikely to join the war because the potential benefits are extremely limited, while the risks for Minsk and Moscow are enormous.