A new strategic assessment argues that foreign troops, legal pledges and peacekeeping missions would fail to deter Russia unless Kyiv can impose heavy costs on a future invasion.
WESTERN promises to protect Ukraine after any peace deal will not deter Russia unless Kyiv is left with a military strong enough to make another invasion prohibitively costly.
The stark warning comes as talks between envoys from Kyiv, Moscow and Washington entered a third day on Friday, with negotiations continuing over the framework of a possible ceasefire.
Western officials are advancing plans for a so-called “coalition of the willing” that could form part of a future ceasefire-enforcement mechanism, with European forces potentially backed by US support if Russia were to mount sustained violations.
But a new report by Sibylline warns that politically fragile or vaguely defined security guarantees could backfire, encouraging Russia to test any post-war settlement and raising the risk of renewed fighting within years of a truce.
“Any peace or ceasefire agreement signed in 2026 may not end the almost 12-year-long Russo-Ukrainian War,” says report author Alexander Lord, Sibylline’s lead Europe analyst.
“If Ukraine has a strong, well-armed military, that creates a single, clear point of deterrence.
“Russia knows exactly who it would be fighting and what the costs would be.”
The assessment argues that Ukraine’s most credible defence would be its own forces, not UN peacekeepers, Western reassurance missions or Article 5-style pledges without NATO membership.
Under the model set out in the report, Ukraine would need to maintain a large active force backed by trained reserves, modern weapons and pre-positioned stockpiles in neighbouring NATO states such as Poland and Romania.
Sustaining such a force would require long-term financial commitments from Western partners at a time when many European governments face competing domestic defence priorities.
The European Union’s recent €90 billion pledge to support Ukraine’s military capabilities underscores the scale of the resources involved, but the report argues that funding Ukrainian deterrence directly may ultimately prove more cost-effective than expanding national forces across Europe to counter a renewed Russian threat.
“Ukraine can’t afford to do it alone, nor does it have the industrial base for the necessary weapons systems. Large spending packages over five- and ten-year periods will likely be needed for this to be truly credible,” Lord adds.
“This may seem obvious to some, but the reality is that — while the funding is a good start — decisions over long-term financing have not really been made yet.”
Beyond this, external guarantees are judged politically fragile
NATO-style protections without formal membership would depend heavily on US willingness to act, something Sibylline treats as increasingly uncertain as Washington’s strategic focus shifts towards China.
Ukraine has proposed abandoning its long-standing goal of joining NATO in return for “Article 5-like” assurances from the US and European allies, but such arrangements would still rely on US leadership and could be vulnerable to political shifts that Russia could exploit.
Plans floated by France and the UK to send troops to Ukraine as part of a post-war reassurance force are also dismissed as unrealistic and potentially counterproductive.
Moscow has repeatedly warned that Western troops on Ukrainian soil would be treated as legitimate targets.
“A Western deployment to Ukraine as part of a peace settlement is a non-starter from Russia’s perspective,” Lord says.
“It flies in the face of one of the fundamental reasons for the invasion in the first place.”
He added that Moscow would likely veto any such proposal in negotiations, making it incompatible with a formal peace deal.
The report says any European-led force would face credibility problems without a US military backstop, particularly around logistics, intelligence and air support, while personnel and equipment shortages across European armies would further limit deterrent value.
A UN peacekeeping mission is also judged unworkable because Russia could veto authorisation in the UN Security Council and Ukraine’s frontline is considered too long to police effectively.
EU membership alone is also described as insufficient as a deterrent, given the bloc lacks NATO’s integrated command structure and military capacity, while fast-tracking Ukraine’s accession remains politically unlikely.
The idea of Ukraine acquiring nuclear weapons is treated as a dangerous wildcard rather than a solution.
While nuclear arms would theoretically deter Russia, the report argues they would more likely provoke Moscow into striking first to prevent such a programme from being completed.
Gen Sir Richard Barrons, former head of Joint Forces Command, said any durable settlement would ultimately depend on building a self-sufficient Ukrainian military rather than relying primarily on foreign deployments.
“The only viable long-term strategy is a robust and independent Ukrainian armed force,” he said.
“There is no credible approach that does not link the transformation of European defence posture with sustained support for Ukraine’s military strength.”
He warned that debates over whether Russia would accept Western troops in Ukraine risked missing the central issue.
“The question is not whether Russia will accept these arrangements. The question is what must be done to ensure Russia is never in a position to attempt this again,” Barrons said.
“If deterrence is not built around that principle, the war risks restarting when Moscow believes conditions are favourable.”