The distinction was established in the jurisprudence of the Court of Justice and is based on the principle of implied liability, the external liability resulting from the existence of internal liability. The treaty confers express responsibility in only two cases: trade policy (Article 133, former Article 113) and association agreements (Article 310, ex-Article 238). The integration and implementation of all EU legislation is the main challenges facing the candidate countries. They require strengthening of legal administrations and systems and a drastic adaptation of the infrastructure of candidate countries to EU standards, particularly in the areas of environment, transport, energy and telecommunications. In order to facilitate these important adjustments, pre-accession assistance is granted to the candidate countries. In October 2004, the Commission adopted a pre-accession strategy for Croatia, where negotiations are expected to begin in 2005. Croatia will be eligible for the three pre-accession financing instruments (Phare, ISPA and Sapard), but the Commission reserves the right to suspend them immediately in the event of a serious and persistent violation of political criteria. After a contract is concluded, written documents that provide formal proof of the agreement to be concluded, as well as reservations and declarations, are placed under the tutelage of a custodian. Unless the treaty is otherwise stated, the tabling of the instruments of ratification, acceptance, approval or accession gives the consent of a treaty-bound state. In the case of contracts with a small number of parties, the custodian is usually the state government in the territory from which the contract was signed. Sometimes different states are chosen as custodians. Multilateral treaties generally designate an international organization or the Secretary-General of the United Nations as custodian. The custodian must accept all communications and documents relating to the contract, verify that all the formal conditions are met, file them, register the contract and communicate to the relevant legal acts to the parties concerned.
The accession of ten new Member States on 1 May 2004 virtually ended their pre-accession strategy.