Whether it was by scorn for the Greeks, or by appreciation of the Servian concentration, the Bulgarians had planned to confront the Servians with four of their five armies. We have already seen that General Ivanoff had the second army alone to oppose to the Greeks, and that even a few battalions of his troops were needed on the Servian flank.
The engagements between the Bulgarians and the Servians had two distinct fields of action, one in Macedonia, and the other on the Bulgaro-Servian frontier.
In Macedonia, the Bulgarians experienced the same surprise in regard to the Servians as in regard to the Greeks. Their sudden attack of June 30th did not strike terror to the hearts of their opponents. Instead of gaining for them a favourable diplomatic position, they found that the Servians did not even suggest a parley. On July 1st, the Servians started a counter-attack, and kept a steady offensive against their former allies for eight days. Gradually the Bulgarians, along the Bregalnitza, gave ground, retreating from position to position, always with their face towards the enemy. The battle, after the first day, was for the Bulgarians a defensive action all along the line.
On July 4th, General Dimitrieff assumed the functions of generalissimo of the Bulgarian forces. He tried his best to check the Servian offensive. But the aggressive spirit had gone out of the Bulgarian army. Lulé Burgas could not be repeated. It was incapable of more than a stubborn resistance to the Servian advance. By July 8th, the Servians were masters of the approaches to Istip, and had cleared the Bulgarians out of the territory which led down into the valley of the Vardar. Then they stopped. From this time on to the signing of the armistice, the Macedonian Servian army was content with the victories of the first week.
Along the Servian-Bulgarian frontier, the Bulgarian army had some initial success. But General Kutincheff did not dispose of enough men to make possible a successful aggressive movement towards Nish. From the very first, when the Macedonian army failed to advance, the Bulgarian plans for an invasion of Servia fell to the ground. They had based everything upon an advance in Macedonia to the Vardar. So the forward movement wavered. The Servians, now sure of Rumanian co-operation, advanced in turn towards Widin. General Kutincheff was compelled to fall back on Sofia by the Rumanian invasion. Widin was invested by the Servians on July 23d.
Rumania had watched with alarm the rise of the military power of Bulgaria. She could not intervene in the first Balkan war on the side of the Turks. The civilized world would not have countenanced such a move, nor would it have had the support of Rumanian public opinion. Whatever the menace of Bulgarian hegemony in the Balkan Peninsula, Rumania had to wait until peace had been signed between the allies and the Turks. But, as we have already seen, during the first negotiations at London, her Minister to Great Britain had been instructed to treat with Bulgaria for a cession of territory from the Danube at Silistria to the Black Sea, in order that Rumania might have the strategic frontier which the Congress of Berlin ought to have given her, when the Dobrudja was awarded to her, without her consent, in exchange for Bessarabia. As Rumania had helped to free Bulgaria in 1877-78, and had never received any reward for her great sacrifices, while the Bulgarians had done little to win their own independence, the demand of a rectification of frontier was historically reasonable. Since Rumania had so admirably developed the Dobrudja, and had constructed the port of Constanza, it was justified from the economic standpoint. For the possession of Silivria, and a change of frontier on the Dobrudja, was the only means by which Rumania could hope to defend her southern frontier from attack.
At first, the Bulgarians bitterly opposed any compensation to Rumania. They discounted the importance of her neutrality, for they knew that she could not act against them as long as they were at war with Turkey. They denounced the demands of Rumania, perfectly reasonable as they were, as "blackmail." They were too blinded with the dazzling glory of their unexpected victories against the Turks to realize how essential the friendship of Rumania—at least, the neutrality of Rumania—was to their schemes for taking all Macedonia to themselves. When, in April, they signed with very ill grace the cession of Silivria, as a compromise, and refused to yield the small strip of territory from Silivria to Kavarna on the Black Sea, the Bulgarians made a fatal political mistake. It was madness enough to go into the second Balkan war in the belief that they could frighten, or, if that failed, overwhelm the Servians and Greeks. What shall we call the failure to take into their political calculations the possibility of a Rumanian intervention? Even if there were not the question of the frontier in the Dobrudja, would not Rumanian intervention still be justified by the consideration of preserving the balance of power in the Balkans? By intervening, Rumania would be acting, in her small corner of the world, just as the larger nations of Europe had acted time and again since the sixteenth century.
The Rumanian mobilization commenced on July 3d. On July 10th, Rumania declared war, and crossed the Danube. The Bulgarians decided that they would not oppose the Rumanian invasion. How could they? Already their armies were on the defensive, and hard pressed, by Greeks and Servians. There is a limit to what a few hundred thousand men could do. It is possible, though not probable, that the Bulgarian armies might have gained the upper hand in the end against their former allies in Macedonia. But with Rumania bringing into the field a fresh army, larger than that of any other Balkan States, Bulgaria's case was hopeless. The Rumanians advanced without opposition, and began to march upon Sofia. They occupied, on July 15th, the seaport of Varna, from which the Bulgarian fleet had withdrawn to Sebastopol.
It would have been easy for the Rumanians to have occupied Sofia, and waited there for the Servian and Greek armies to arrive. The humiliation of Bulgaria could have been made complete. Why, then, the armistice of July 30th? Why the assembling hastily of a peace conference at Bukarest? Political and financial, as well as military, considerations dictated the wisdom of granting to Bulgaria an armistice.
Greece and Servia were exhausted financially, and their armies could gain little more than glory by continuing the war. The Greek army, in fact, was in a critical position, and ran the risk of being surrounded and crushed by the Bulgarians. The Servians had not shown much hurry to come to the aid of the Greeks. The truth of the matter is that, after the battle of the Bregalnitza, which ended on July 10th, the Servians began to get very nervous about the successes of their Greek allies. They knew well the Greek character, and feared that too easy victories over the Bulgarians might necessitate a third war with Greece over Monastir. So, on July 11th, with the ostensible reason that such a measure was necessary to protect their rear against the Albanians, the Servian general staff withdrew from the front a number of the best regiments, and placed them in a position where they could act, if the Greeks tried to seize Monastir. On the other hand, Rumania gave both Greece and Servia to understand that she had entered the war, not from any altruistic desire to help them, but for her own interests. To see Bulgaria too greatly humiliated and weakened was decidedly no more to the interest of Rumania than to see her triumphant.