Complex sentence: The conference would lead to the Treaties of Rome being signed on 25 March 1957 which established the European Economic Community (EEC) and the European Atomic Energy Community (Euratom) among the members of the ECSC.
Split into simpler sentences: The conference would lead to the Treaties of Rome being signed on 25 March 1957. They established the European Economic Community (EEC) and the European Atomic Energy Community (Euratom) among the members of the ECSC.