WASHINGTON (Reuters) – The U.S. Senate on Wednesday approved Finland and Sweden’s accession to the North Atlantic Treaty Organization (NATO), the most significant expansion of the military alliance since the 1990s, in response to the invasion of Ukraine from Russia.

Senators approved the measure by 95 votes to 1, far exceeding the two-thirds majority (67 votes) required to support the ratification of the two countries’ instruments of accession to the nuclear-armed, US-led alliance.

Finland and Sweden have applied for NATO membership in response to Russia’s invasion of Ukraine, which has repeatedly warned not to join the alliance.

NATO’s 30 allies signed the new members’ accession protocol last month, which allowed them to join the alliance after member states ratified the resolution.

Membership must be ratified by the parliaments of all 30 NATO members in order for Finland and Sweden to be protected by a defense clause that says an attack on an ally is an attack on everyone.