I dag skrivs en viktig sida i Europas historiebok. Storbritannien påbörjar en två år lång process som leder till skilsmässa från den Europeiska unionen.

Debatten kring brexit har fokuserat på kortsiktiga reflektioner: kostnader, processer och marknadsreaktioner.  Få har lyft fram det historiska med  britternas beslut.

2019, när Storbritannien lämnar EU, är ett lika historiskt år som 1952 när kol­ och stålgemenskapen grundades, eller 1989 då det kalla kriget tog slut.

I varje kris finns en möjlighet. Själv tycker jag att EU borde reagera på fem sätt.

1. Fortsätt utvidgningen.

Det blir första gången som en medlems­stat lämnar EU. Detta har aldrig skett tidigare. EU har varit som Eagles­låten Hotel California: ”You can check out any time you like, but you can never leave”.

Nu lämnar britterna EU, men detta bör absolut inte bli en broms för vidare utvidgningar. Tvärtom.

Utvidgningen har lätt till demokrati och marknadsreformer på hela kontinenten.

2. Försvara EU:s värderingar.

Efter brexit och valet av Donald Trump söker den fria världen nya ledare.

Stommen till EU:s värderingar – demokrati, frihet, jämställdhet, rätts­staten och mänskliga rättigheter – är viktigare än någonsin.

EU har lyckats främja fred, säkerhet, välfärd och stabilitet baserade på dessa värderingar. Nu, mer än någonsin, krävs det ryggrad och mod av ledande politiker att fortsätta försvaret.

3. Vårda EU:s fyra friheter.

Storbritannien har varit en viktig drivkraft i liberaliseringen av EU:s inre marknad.

Fria rörligheten av varor, service, arbetare och pengar har varit grunden till Europas ekonomiska tillväxt och därmed finansieringen av gemene välfärdsstat.

I en värld av ekonomisk populism och protektionism, måste marknadsvänliga EU­länder ta över när britterna lämnar ifrån sig stafettpinnen.

4. Satsa på säkerhet.

Storbritannien är medlem i FN:s säkerhetsråd och Nato. EU tappar en global spelare samtidigt som USA:s presidentkräver att Europa tar mera ansvar för sitt eget försvar. Gör det då.

EU länderna bör fördjupa säkerhets­samarbetet och se till att britterna är med alltid när det är möjligt. Detta borde gynna länder som Sverige och Finland som tyvärr står utanför Nato.

5. Reflektera om EU:s framtid.

På ett sätt har reflektionen redan börjat. Kommissionen har lagt ut fem alternativ och EU ledarna skrev under en deklaration Romfördraget till ära. En bra början, men inte tillräckligt.

Det går bara inte att fortsätta med samma dubbelmoralistiska retorik. Det går inte att skälla på EU varje gång det gäller något negativt och hylla sig själv när någonting lyckas. Brexit är inte EU:s begravning, även om jag tycker att det är ett av det dum­maste besluten som Storbritannien har fattat efter andra världskriget.

Det kan bli en ny början, precis som 1952 och 1989. Europa har inte råd med nationalism och protektionism. Själv tror jag att brexit och Donald Trump kan vara just det som EU behövde  i populismens och antiglobalismens tidevarv – en väckarklocka.

I remember being one of the few pro-Europe government ministers to give a thumbs up to David Cameron’s gamble on a referendum on EU membership. I felt it was time for the reluctant bride to reaffirm its vows. I was sure the marriage would last. My British wife thought differently, that it would spell disaster.

I never believed the UK would leave the EU. I always felt British rationality would prevail over the emotion and fake news linked to membership. But I was wrong, my wife was right. On Wednesday, as divorce proceedings begin, many will ask whether this is the beginning of the end, or the end of the beginning for both the UK and the EU.

Analysis has been focused on the short-term impact of Brexit — the cost, timing and transition — rather than its historical effect. At the end of the day, I believe we will all be worse off, but in every crisis lies an opportunity.

On the Richter scale the referendum ranks with the biggest of earthquakes in international politics. In historical significance, Wednesday’s letter of exit stands next to the founding of the European Coal and Steel Community in 1952 and the end of the cold war in 1989. Here are three reasons why.

First, never before has a fully fledged member left the EU. Yes, Greenland did leave and took with it immense amounts of fish, but it is not an independent country. The EU’s appeal has always been such that nations have wanted to join it, not leave.

In many ways enlargement has been the Union’s most successful policy as it expanded from the original six to 28, with another dozen hoping to join the club one day. The prospect of membership has led to democratic transformation and economic reform in many hopeful nations. Eastern and Central European countries competed to be first to fulfill the accession criteria.

So will Britain’s exit make the EU less alluring? Perhaps, but it will not stop the Balkans and others from pursuing entry to the world’s biggest market and most successful peace project. Nor will it lead others to leave — the cost is simply too high.

Second, Brexit will allow the members to pursue deeper integration — if they so desire. Many countries have used the UK as a smokescreen and will lose their best excuse for less pooling of sovereignty. Yet I actually think there is not much appetite now for a leap towards ever closer union.

There has been a lot of jibberish about differentiated integration as the UK leaves. But that was already allowed for by the rules of enhanced co-operation. We will see more flexibility inside the EU, but no core Europe outside. The DNA of European integration has been based on the sometimes uncomfortable balance between deepening and widening. Before every expansion, integration has deepened; it happens before enlargement, not after exit.

Finally, Brexit will force the EU to think about its own future. The European Commission’s five options for the Union and the declaration celebrating the 60th anniversary of the Treaty of Rome are steps in the right direction. Will they be enough? Probably not, but they are a good start.

Reform is never easy, particularly when it involves pooling sovereignty and sharing responsibility on a supranational level. The blame game never ends; local politicians accuse national decision makers who in turn point their finger at Brussels. Yet most understand that there are only common solutions to common problems. And co-operating in one area usually leads to pressure to do so in another.

After the EU loses a nuclear power and permanent member of the UN Security Council, it will have to deepen co-operation on defence, and this will follow through on immigration and asylum policy. That is how the coal and steel community moved towards an economic community, customs union, single market, European union, common currency and banking union.

The Union’s main goals — peace, prosperity, security and stability — are more important than ever. The big question is how to organise the EU’s work to best serve its almost half a billion people. Brexit will have a potential ideological impact — the Union will lose a market reformer, free trader and strong advocate of the single market. In an age of economic populism and protectionism, like-minded countries will have to defend its four basic freedoms on the movement of goods, services, labour and money.

I believe the EU and its leaders should seize the moment after Brexit, pursue a serious round of self-reflection and reform accordingly. There was a great case for European integration and co-operation in 1952 and 1989. That case remains as strong as ever, especially after Brexit in 2019.