No tribute, no peace
Summer, 1967 A.D.: Greece proposes a third peace treaty with the same terms as the second. After much deliberation, the Norse parliament responds that they will agree, if Greece pays a large ransom and ongoing tribute. The Greeks prove they didn't want peace that badly after all, and the war continues.
Well, I gave peace a chance. With the way this is going, the survival of their entire empire is on the line. I have enough momentum to probably push them all the way back to their capital, and from there, into the sea. My conditions were generous, but I guess they're just too prideful to accept someone else's terms.
Winter, 1967 A.D.: Greece rolls out their own modern bombers, as well as the world's first rocket artillery. They hit Norse positions near Munich, taking out most of the NDU artillery stationed there. New SF-67 fighter jets are deployed to counter any future air raids.
On the Western front, combined air and sea assaults by the NDU wipe out Greece's foothold at Sicyon.
Summer, 1968 A.D.: The NDU perfects rocketry, and immediately retrofits their artillery to match that of Greece. On the other side of the same base, Firestar I, the world's first atomic bomb, is completed. It begins the long trek to Munich airfield. The science and engineering teams responsible for its construction turn their efforts immediately to getting the Norse space program off the ground.
To the South, the NSS relocates its spies from the soon-to-be-a-crater city of Hamburg to Athens and Sparta, in the heart of the ancient Greek homeland. The Norse fleet begins bombarding Chios.