These included measures in the security sphere (e.g. arrangements for receiving, storing and using classified information), as well as in areas such as air defence, infrastructure, force planning and communication and information systems. However full integration of the new member countries is an ongoing process calling for continuing efforts over a longer period.

The main stages leading up to the accession of the Czech Republic, Hungary and Poland were as follows:

- 10 January 1994. At the NATO Summit in Brussels, the 16 Allied leaders said they expected and would welcome NATO enlargement that would reach to democratic states to the East. They reaffirmed that the Alliance, as provided for in Article 10 of the Washington Treaty, was open to membership of other European states in a position to further the principles of the Washington Treaty and to contribute to security in the North Atlantic area. - September 1995. The Alliance adopted a Study on NATO Enlargement. Without giving fixed criteria for inviting countries to join, the Study described a number of factors to be taken into account in the enlargement process. It also stipulated that the process should take into account political and security-related developments throughout Europe. The Study remains the basis for NATO's approach to inviting new members to join.

- During 1996, an intensified individual dialogue was undertaken with 12 interested Partner countries. These sessions improved their understanding of how the Alliance works and gave the Alliance a better understanding of where these countries stood in terms of their internal development as well as the resolution of any disputes with neighbouring countries. The Study identified this as an important precondition for membership.

- 10 December 1996. The NATO Allies began drawing up recommendations on which a country or countries should be invited to start accession talks, in preparation for a decision to be made at the Madrid Summit of July 1997.

- Early 1997. Intensified individual dialogue meetings took place with 11 Partner countries, at their request. In parallel, NATO military authorities undertook an analysis of relevant military factors concerning countries interested in NATO membership.

- 8 July 1997. Allied leaders, meeting in Madrid, invited three of the countries - the Czech Republic, Hungary and Poland - to start accession talks with the Alliance.