Evolution of the "European Union" equilavent in my TL-ish thingy.
1979: Formation of the Visegrad Pact via the Treaty of Visegrad. With the Baltic Kingdom, Kingdom of Poland, Kingdom of Bohemia, Slovak Republic and Republic of Hungary as founding members (only permanent organ the Secretariat was headquartered in Krakow, lead by a Secretary-General chosen by the heads of government of member states). The organisation also mandated annual (or more frequent) meetings of the Heads of State, Heads of Government and Ministers of member states. In the three years before it evolved into the Intermarium Organisation the Pact passed a Common Energy Policy and Common Agriculture Policy, alongside some other common rules and regulations.
1981: Croatia joined the Visegrad Pact with the Treaty of Budapest.
1981: Treaty of Riga reforms the Visegrad Pact into the Intermarium Organisation with Finland and Denmark joining the 6 members of the Pact as founding members of it. Intermarium Organisation added an interparliamentary assembly under the name Senate with some legislative authority. A High Court to oversee the Organisation was also established with the justices appointed/approved by the Senate. Intermarium also had a Joint Chiefs of Staff for closer military cooperation. Throughout its lifetime the Intermarium Organisation instituted a Common Baltic Fishing Policy as well as a Free Trade Area.
1983: Sweden accedes with the Treaty of Stockholm.
1983: Bosnia, Montenegro and Albania join Intermarium with the Treaty of Zagreb.
1985: Romania and Bulgaria accede with the Treaty of Krakow.
1985: Intermarium Organisation and the German Empire form the European Council and European Cooperative Organisation with the Treaty of Berlin (thought German Guiana was not included). With the military/political alliance aspects taken over by the EC and economic and social aspects by the ECO. The seat of the High Court is moved from Krakow to Prague while the Senate is moved to Vienna. A directly elected European Parliament is also established in Vienna (creating a bicameral system of sorts with the Senate and the Parliament). The Council of Heads of Government is renamed the High Council. The High Council elects a "Chancellor" who is the leader of the European Council as a whole. These institutions are common between the EC and ECO. Joint Chiefs of Staff composed of member state chiefs of defense is replaced by the European Council General Staff headquartered in Bratislava/Pressburg, lead by a Director General. While European Cooperative Organisation Commission was established as an executive body also seated in Bratislava/Pressburg. The institution of the Councils of Ministers is also retained for the ECO.
1987: Treaty of Copenhagen sees accession of France, Basque Republic, Catalonia, Malta, Greece and Turkey.
1989: Treaty of Paris, Spain and Portugal join the EC/ECO (Portuguese Sao Tome and Principe, Cabinda and Macau not included).
1991: Treaty of Rome, Italy joins EC/ECO (Italian Indian Ocean Territory not included). Decision is taken to allow ECO membership without also being a member of the EC. San Marino,Vatican, Switzerland, Norway, Andorra, Iceland and Serbia join ECO but not the EC with the Treaty of Vienna (Switzerland and Norway rejected full membership via referendum before the EC-ECO split was decided on, Serbia applied for EC membership but was rejected for the time being thought allowed into the ECO). Throughout the 90s a customs union and common market is established within the ECO as well as visa liberalisation.
1997: European Council gains four members as Ireland joins with the Treaty of Dublin, Serbia with the Treaty of Belgrade, Andorra with Treaty of Barcelona and San Marino with Treaty of Milan.
2004: Iceland acceeds to the EC with the Treaty of Reykjavik. Open Borders between member states established in the 2000s.
2015: Estonia and Brittany secede from the Baltic Kingdom and France, respectively.
2016: Before the transitional period (establishment of border controls, tariffs etc) ends they apply for membership in their own right and rejoin with the Treaty of Brussels.
2022: Treaty of Constantinople/Istanbul, Georgia joins the European Cooperative Organisation without joining the European Council.
(Establishing a common currency like the OTL Euro and a common Central Bank is within EC/ECO agenda as a (near) future goal to achieve but has not been achieved unlike OTL.