Exactly, when the king took over...he messed it up.
That's an over simplication.
Here are a few points I'd like to make:
1. The Nationalist forces, despite being overwhelmed, adopted a different approach. Simply, the Turks, who had historically always been unfamiliar/incompetent at retreats, finally learned how conduct a proper defensive war. The Turks also adopted a clever defense in depth doctrine: "There is no defense of a line, but there is the defense of the superficies”, as Ataturk told his soldiers. The Greek army never managed to encircle the Nationalists.
2. By 1921, the Greek army was exhausted and low on morale. The Greek army had reached its culminating point (especially after being halted at Inonu by Ismet Pasha).
3. Constantine was unpopular with the Allies, who then cut off military aid to Greece after he came to power.
4. By 1921, the Nationalists managed to quell internal rebellions (Ethem the Circassian), bested the Armenians, pacified the French and Italians, and reached agreements regarding its Eastern borders (Kars and Moscow agreements). Add to that arms and gold from Central Asia and the Soviet Union, and the fact that many of the troops in the East were freed up, the Turkish position became stronger.
5. [Continuing on point 2) It was only with some pause and fresh reinforcements that the Greeks, depite exhaustion and extended supply-lines, were able to press on. The Greeks were on the verge of victory in late 1921...
6. ... Depite Soviet ammunition, supplies were still short on the Turkish side and the Greeks still had the advantage in numbers but they choose the defensive strategy of occupying strategic points in Central Anatolia, rather than taking the risky choice of pursuing the Turks all the way to Ankara. I suppose this could be do to the poor judgement of the generals or to the fatigue of the soldiers. However, the Greeks were not the only ones to have poor generals ...
7. The Nationalists had a change in leadership. Ataturk and Fevzi Cakmak took over the army from the heavily criticized, Ismet Pasha... and they went on to repel the Greeks at Sakarya (which is why they are the only two generals in the Republic's history to earn the title of "Field Marshall").
8. Once again the Greeks reached their culminating point and the Turks opted for a risky counter-attack (summer 1922). This time the Turks had the advantage in artillery and cavalry, even though the Greeks had more infantry and possessed strategic heights. The Turkish army was divided in two, with the cavalry ordered to circle round the back of the Greeks and wreack havoc on Greek communications and bases. The Turks managed to win after one week of fighting.
In short, the Turks cleverly secured their other flanks and mobilized all their resources to combat Greece, whereas Greece lost the favor of the Allies. The Turks also had better generals and a better plan - the Greeks charged ahead when they shouldn't have and stopped when they should have went forward.
And this is military 101:
- The defender will eventually even the scales because their supply-lines shorten with every retreat. Visa-versa is true for the attacker.
- Every victory demoralizes the attackers because the soldiers get fed up with fighting.
- Turks make the finest soldiers in the world if lead properly.
"It is a dangerous thing to be a Machiavelli. It is a disastrous thing to be a Machiavelli without virtū."
- Hans J. Morgenthau