HELSINKI — Finland received the green light to join NATO when Turkey ratified the Nordic country’s membership late Thursday, becoming the last country in the 30-member Western military alliance to sign off. All NATO members must vote unanimously to admit a new country into the alliance. The decision by the Turkish parliament followed Hungary’s ratification of Finland’s bid earlier in the week. The addition of Finland, which shares a 1,340 kilometer (832 miles) border with Russia, will more than double the size of NATO’s border with Russia. However, a few more steps and procedures are required before the northern European nation becomes the 31st full NATO member: [time-brightcove not-tgx=”true”] Acceptance letters Turkey and Hungary dispatch acceptance letters to the United States which is the depositary, or safekeeper, of NATO under the alliance’s 1949 founding treaty.