not quite a declaration of war by the UN

Words matter to diplomats and lawyers. So when the UN Security Council voted unanimously to condemn the terrorist actions by ISIL and others in Paris, Beirut, and elsewhere policymakers pondered the careful wording.

UNSC Resolution 2249 says, in a key paragraph:

5.   Calls upon Member States that have the capacity to do so to take all necessary measures, in compliance with international law, in particular with the United Nations Charter, as well as international human rights, refugee and humanitarian law, on the territory under the control of ISIL also known as Da’esh, in Syria and Iraq, to redouble and coordinate their efforts to prevent and suppress terrorist acts committed specifically by ISIL also known as Da’esh as well as ANF, and all other individuals, groups, undertakings, and entities associated with Al-Qaida, and other terrorist groups, as designated by the United Nations Security Council, and as may further be agreed by the International Syria Support Group (ISSG) and endorsed by the UN Security Council, pursuant to the statement of the International Syria Support Group (ISSG) of 14 November, and to eradicate the safe haven they have established over significant parts of Iraq and Syria;

A bit wordy,sure, touching many bases as required by a compromise document that all members could support. And as such it can be cited by the French, the British, the Americans,and the Russians if they want to conduct air strikes against ISIL.

But it's also important to realize what's missing from this tough-sounding document. The key omission is any mention of Chapter VII of the UN Charter, the section authorizing the use of force in the name of the international community. That was a bridge too far for several UNSC members, especially those who felt that the U.S and NATO went too far under the Libya resolution [UNSC 1973] in 2011. That measure said:

Acting under Chapter VII of the Charter of the United Nations,

1.

1 Demands the immediate establishment of a cease-fire and a complete end

to violence and all attacks against, and abuses of, civilians;...

6.Decides to establish a ban on all flights in the airspace of the Libyan Arab Jamahiriya in order to help protect civilians;

The UN words are helpful but still limited.