The most striking number in a hypothetical enlarged Europe is about $27 trillion. The more important number may be €470 billion.
The first is the rough nominal output of a bloc combining the EU, Britain, Switzerland, Norway and the rest of the European accession belt through Ukraine. The second is the European Commission's estimate of additional financing that companies could raise if Europe's capital markets became more integrated.
That distinction matters because size is not Europe's main shortage. Integration is.
World Bank data put the EU at about $21.24 trillion of GDP in 2025 and Britain at just over $4 trillion. Add Switzerland, Norway, Ukraine, the Western Balkans, Moldova, Iceland and Liechtenstein and the system approaches $27 trillion, with around 590 million people. It would sit close enough to the United States to count as a peer economic bloc and well above China in nominal dollar terms.
Yet the United States would still possess an advantage that does not appear in a simple GDP table. American savings, government debt, venture capital, stock markets and corporate finance operate inside one federal system. A company in Texas or Massachusetts does not need to treat the other state as a separate capital jurisdiction.
Europe remains different. It has London, the continent's largest international financial centre, outside the EU. Zurich is similarly connected but institutionally separate. Inside the Union, insolvency rules, taxation and retail investment practices still differ significantly by country.
A serious enlargement would therefore succeed only if it became an integration project, not a membership project. The commercial prize would be a capital system able to connect British and Swiss financial depth with the industrial base of Germany, France, Italy and Central Europe, the energy strengths of the Nordic region, and the reconstruction needs of Ukraine.
Ukraine is especially revealing. Its 2025 GDP was roughly $214 billion, so accession would barely move the $27 trillion total. But rebuilding the country has been estimated at almost $588 billion over a decade. That creates a huge demand for project finance, insurance, infrastructure investment and industrial capital. If the reconstruction programme is integrated into European capital markets, the spending is not simply aid. It becomes an investment pipeline.
The same logic applies to defence. EU states spent €418 billion on defence in 2025, with €454 billion projected for 2026. Britain and Norway would add more capacity. But a larger budget fragmented across national procurement systems can still deliver less strategic output than a smaller unified market.
The economic case for a wider union is therefore strongest where integration eliminates duplication. One securities market is more useful than several deep but separated ones. A shared energy network can absorb regional shocks better than national systems. Defence companies can invest more confidently when procurement standards converge. Technology companies can scale faster when they face one large market rather than overlapping rulebooks.
This is where the thought experiment stops being fantasy. Europe already has the institutional core of such a system: a single market of about 450 million consumers, free movement and common regulation in many fields. The question is whether the next stage of enlargement would deepen that machinery or merely stretch it.
For Britain, the strategic choice is particularly sharp. A continent-sized European capital and industrial system would be more powerful with London inside its architecture, while London would gain access to a larger pool of continental savings, projects and companies. The same would be true for Switzerland.
A $27 trillion Europe would be formidable on a spreadsheet. Its real power would emerge only if capital could move through it as easily as goods already do across much of the single market. The project becomes historic not when Europe adds another state, but when it makes several financial and industrial centres behave as one economic system.