The French Were Against an Offensive on the Macedonian Front
From the moment that they lost their homeland, the Serbians were ready to launch an offensive to get it back. The French were less than eager to start a huge offensive on the Macedonian Front because they believed that victory on the Western Front was more important and they wanted to protect their own homeland. The Serbian Army had been forced to evacuate by sea and then come back on land to form a front line in Allied territory.
From the moment they had been chased from their homeland, they wanted to go back and reclaim it. The problem was that since they were kept from their own home they had no way to supply their army and completely depended on the French for supplies and to keep up their artillery.
The French, however, where unwilling to expend their resources on the Balkans because they saw it as far less important than what was at stake on the Western Front. Prime Minister Georges Clemenceau wanted to keep the resources and the men he had for the fighting in Western Europe. The French decided to let the Serbian artillery fall into disrepair over the two years on the same front line. They insisted on the French manning the heavy weapons and leaving the Serbians to handle the light artillery and trench mortars.
Finally, in 1918, the Serbians got their wish as the Allies decided that it was time for a massive offensive on the Macedonian Front. The French finally took the time to repair and supply the Serbian artillery and to properly outfit the troops. There is no way of knowing how the battle and the war might have turned out if the French and the rest of the Allies had been willing to plan an offensive earlier, but it was a huge turning point by the end of 1918.