Great symbolic importance is given to the fact that it is the first Summit convened in the new headquarters of the Alliance, which has so far cost 1.3 billion Euros or $1.5 billion (but the real price, 7% of which is borne by Italy, is still to be established): it’s a structure of over 2.5 million square feet, almost double the previous one, where a permanent staff of about 4,000 military and civilians works, equipped with 18 large halls where more than 5,000 meetings are held annually with an average participation of 500 guests per day. The structure, currently made up of eight major wings and four minor wings connected to a long central body, is of a modular type: therefore expandable as NATO continues to expand.

In 1990, on the eve of the dissolution of the Warsaw Pact, US Secretary of State James Baker assured USSR President Mikhail Gorbachev that "NATO will not extend by a single inch to the East". But in 1999, while demolishing the Yugoslav Federation with the air war, NATO included the first three countries of the former Warsaw Pact: Poland, the Czech Republic and Hungary. Then, in 2004, it extended to Estonia, Latvia, Lithuania (formerly part of the USSR); Bulgaria, Romania, Slovakia (formerly members of the Warsaw Pact); and Slovenia (formerly part of the Yugoslav Federation). In 2009, it included Albania (once a member of the Warsaw Pact) and Croatia (formerly part of the Yugoslav Federation); in 2017, Montenegro, also part of the Yugoslav Federation.

After having expanded in 1999-2017 from 16 to 29 members, NATO leaves "the door open" to other entrances: Ukraine and Georgia, already part of the USSR, are waiting to enter; Bosnia-Herzegovina and Macedonia, already part of the Yugoslav Federation. For this reason, NATO has set up an expandable headquarters.

Translation
John Catalinotto
Source
Il Manifesto (Italy)