Horror, unease and questions for US allies as Trump's big shift puts European security in doubt

We are witnessing one of the biggest shifts in geopolitics since the Second World War.

This week one of the fundamental assumptions underpinning European security was put in doubt.

American military might has underwritten the defence of Europe since 1945 - Donald Trump says that can no longer be America's primary focus.

Follow latest: Ukraine casts doubt on US peace plan

But there is a lot more to give America's European allies grounds for profound unease. The most immediate concern is over Ukraine.

Trump has surrendered much of his leverage over Russia before potential peace talks even begin - in a way that rips up his own rules of negotiation.

Observers are horrified.

Nigel Gould-Davies, a Russia expert at the International Institute for Strategic Studies (IISS) thinktank, put it this way: "A major shift in US policy towards a dangerous war appears to be driven by impulse and instinct rather than a disciplined, coordinated inter-agency process - a product not of careful thought, but of the last person to have the president's ear. Putin will work hard to make sure this person is him."

His misgivings are shared many times over in Kyiv.

One Ukrainian put it like this: "It is terrifying to think what Russia could do with a fully mobilised war machine after accumulating military strength for two or three years.

"They have already learned from their mistakes in Ukraine."

Should Putin agree to a ceasefire it seems highly likely he would use it to rearm and recover - then come back for more.

Few defence experts believe an international deterrence force shorn of American troops and NATO Article 5 protection would put him off.

It is not just European security and Ukraine straining US-European relations.

There's Trump's threat to slap massive tariffs on our economies, which would make us all a lot poorer, his decision to pull out of climate change agreements, and his outlandish plans for Gaza - not to mention shutting down US aid which will no doubt cost huge numbers of lives.

All of that puts him at odds with European leaders.

They must now decide - do they dare stand up for their values against this president and risk being punished? Or turn a blind eye, hunker down and try to weather four more years of this?

But there are more fundamental questions for America's allies now.

Is the US a reliable partner anymore under such an unpredictable president? Would China be a less capricious choice perhaps?

Read more:
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Ukraine has every reason to be worried

It is a hugely momentous moment for what is called the "rules-based post-war world order" that has kept us relatively safe and prosperous for the last 80 years.

The way European governments respond will affect all our futures.

(c) Sky News 2025: Horror, unease and questions for US allies as Trump's big shift puts European security in doubt<