BRUSSELS (Reuters) - Leaving the European Union, to be triggered by Prime Minister Theresa May on Wednesday, may transform Britain but it will also change the EU. Here's how:
The Union's budget accounts for only 2 percent of public spending in the bloc. But in the east, transfers from Brussels contribute a much bigger share - some 8 percent of Poland's budget and nearly a fifth of Bulgaria's.
Without Britain, Brussels will have about a sixth less to give to countries that are net recipients, setting up a fight between east and west over a 7-year spending plan from 2021.
In the short term, there will also be a battle with Britain over what it owes on leaving. London may choose to keep paying for access to some key EU budgets, such as for research. But big accounts, like farm subsidies, could be in for radical review.
Britain has used its 12-percent share of EU votes to curb Brussels spending and push hard for free trade. Its departure worries smaller northern allies like the Nordics and Dutch.
Poorer easterners, whose membership Britain championed, fret that Germany and France may stiffen barriers to their low-wage workforce or beef up EU federal powers the ex-communist states dislike. Aspiring new members, notably in the Balkans, also lose an ally against rich westerners wary of further EU enlargement.
The 19 euro countries will lose a key block on their caucus power. They can now outvote non-euro states, but only just. A non-euro bloc led by Poland and Sweden would need major dissent among euro countries to prevent the euro zone setting EU policy.
France becomes the EU's only nuclear-armed, veto-wielding U.N. Security Council member and loses a dogged opponent of its ambitions for more EU defense cooperation outside the U.S.-led NATO alliance; defense is already back on Brussels' agenda.
Germany, ambivalent about being seen as dominating Europe by dint of its economic muscle and being home to nearly one post-Brexit EU citizen in five, is uneasy about how to maintain balance, notably with economically struggling co-founder France.
The EU loses a hefty interlocutor with the United States and the wider English-speaking world. A historic diplomatic and military force, Britain's insight and influence with powers like China and Russia or in the Middle East have been useful to the EU. In Africa, a source of growing concern over migration, British aid budgets and other clout have played a key role.
London's tough line with Moscow has won it friends among the likes of the Baltic states and the Netherlands, which fear that a softer approach from France, Italy and, possibly, Germany will undermine a consensus for pressuring Russia with sanctions over its actions in Ukraine or for cutting dependence on Russian gas.
Though under-represented in the staff of EU institutions, British officials over 44 years of membership have established a key role in senior positions as well as in the EU parliament. That will disappear as British citizens are shut out of EU jobs.
Many governments, notably from smaller states, value what they see as a British approach to administration that is more pragmatic and laissez-faire than the more centralized, dirigiste tradition embedded in the French foundations of the Union.
Britain will leave one legacy likely to survive in the form of English as Brussels' working language, despite some hopes in Paris of restoring the prominence of French.
Since the Brexit vote, EU leaders speak of a renewed unity among the remaining 27. Polls suggest popular support for the EU has broadly increased. But unity will be sorely tested by Brexit negotiations, with governments all having differing priorities.
The unprecedented use of Article 50 of the EU treaty breaks a taboo and means invocations of an "indivisible Union" now ring hollow. Brussels will have to contend with more threats to quit, coloring decision-making across the board for years to come.
Additional reporting by Waverly Colville; editing by Andrew Roche