Britain may not be at war, but the backdrop to next Monday’s strategic defence review is the greatest geopolitical uncertainty since 1945. A set of loosely interconnected conflicts – led by Russia’s continued assault on Ukraine and its related shadow war in Europe, and Israel’s seemingly unending war on Hamas, which may lead to an attack on Iran – have not at all been restrained by a skittish White House with little interest in helping to promote peace in Europe.

One of the three-strong review team is Fiona Hill, who was briefly and famously an adviser to Donald Trump in his first term. She is so worried about the disintegration of postwar norms that she believes the world is drifting towards a “scenario that you had in world war one” where, in the run-up to the war, “suddenly all these different interests and these different conflicts became, you know, basically intertwined with each other, [and] it becomes extraordinarily hard to disentangle”.

Solving problems like these is likely to be beyond the ability of the 130-page document, jointly written by Hill, George Robertson, a former Nato secretary general, and Richard Barrons, a retired British army general. But its remit has been helped by the fact that difficult decisions about which equipment programmes to invest in and to cut have been deferred to a separate command paper in the autumn. Meanwhile, headline budgets to increase defence spending to 2.5% of GDP by 2027 have already been announced by the prime minister, in February.

“What I’m expecting is that it’s basically going to be an essay,” said Lawrence Friedman, a military strategy expert and emeritus professor at King’s College London. Even so, the defence review has been rewritten several times since it was first completed in the spring, partly as a result of drafting battles across Whitehall. Another document – a national security strategy from Keir Starmer’s national security adviser, Jonathan Powell – is due out in June.

In the past, defence reviews have done a poor job of prediction. Boris’s Johnson’s 2021 integrated review, published in the aftermath of Brexit, emphasised a British tilt to the far-off Indo-Pacific, supported by occasional flag-flying visits from the Royal Navy’s two new aircraft carriers that cost £6.2bn. But with Britain pouring more than £3bn a year of arms into Ukraine, the last review’s goal to have a “greater and more persistent presence” than any other European country in the Indo-Pacific looks irrelevant.

This review’s principal task is likely to be descriptive, though it runs into two difficulties: people and money. Statistics out this week show again that more people are leaving the military than joining. Army numbers are at a 300-year low of 70,860, down 2.3% over the past year, despite the backdrop of the war in Ukraine. The numbers of RAF and naval personnel have fallen by similar proportions, meaning that, according to one naval source, the navy can crew only four of its six Type 45 destroyers.

The news flow around service life is dominated by stories about rape, sexual harassment and sexism across the military. Internal reviews over the last two years acknowledged misogyny and misconduct in the Red Arrows and the submarine service. In an inquest into the death of 19-year-old Gunner Jaysley Beck in February, the court found she killed herself after being assaulted and subsequently subjected to unwanted sexual attention. It prompted an outpouring of reports on online forums and social media from mostly female soldiers describing similar negative experiences.

A commitment will be made in the defence review to invest a further £1.5bn in military accommodation, including urgent renovation for the 1,000 worst homes, a longstanding source of complaint. But in recent years the British military has had relatively few positive stories to tell, not least because it has been relatively inactive on operations, with the fraught rescue from Kabul in August 2021 the most significant recent effort. It was followed by the smaller airlift of 2,450 Britons and other western nationals from Sudan in the spring of 2023 as a civil war broke out.

Although Labour promised a modest increase in defence spending in February, amounting to £5.3bn a year in real terms when the increase from the current 2.33% of GDP to the promised 2.5% goes through, the Ministry of Defence (MoD) has an extraordinary capacity to soak up money. A former senior insider estimated that the MoD faced £5bn of cost pressures for next year, partly as a consequence of higher pay settlements announced by Labour, such as this year’s 4.5%. There remains £16.9bn of unfunded commitments in the MoD’s 10-year equipment plan.

Spending on nuclear weapons is rising sharply: analysis by Steve Barwick, of Rethinking Security, concluded that the forecast cost of MoD’s Defence Nuclear Organisation’s 10-year equipment plan increased by 62% to £99.5bn in 2023. The most recent figure, for 2025, was more than £100bn, according to the MoD. At the same time, the challenge of maintaining the UK’s ageing fleet of Vanguard submarines, which carry the Trident nuclear armed missiles, means individual patrol boats are undertaking record missions underwater, the last of which was 204 days long – more than nine months.

A more immediate problem for the British military is how to resource and sustain a commitment to participate in a European-led “reassurance force” for Ukraine, currently promised in the event of a durable ceasefire, if Russia can be persuaded to agree. A British contribution might amount to a brigade of a few thousand, as well as some command and control functions, though finding the troop numbers is likely to be a stretch, suggesting there will be more calls for extra spending.

“To be credible, the defence review needs to be backed by a cast-iron commitment to take defence spending to 3% of GDP by a specific date and 3.5% by 2035,” argued Peter Ricketts, a former national security adviser. But while no extra money is expected immediately, the financial debate may be moved forward not by the review but by Nato and Trump by the end of the month.

Alliance members are considering a proposal from Mark Rutte, Nato’s secretary general, to be tabled at its June summit in The Hague, to increase core defence spending to 3.5% by 2032, with a further 1.5% on cyber and transport and other military-related infrastructure. That would match Trump’s demand that Nato members spend 5% of GDP on defence. “I assume that in The Hague we will agree on a high defence spend target of in total 5%,” Rutte said this week.