In the case of the Third Punic War, Rome blamed Carthage for violating the terms of the previous treaty by making war on the Nubians.

I tried using Polybius but it appears most of his work on the Third Punic War was lost, so the below is from Appian.

The third and last Punic war of the Romans in Africa followed it. The Carthaginians having suffered this calamity at the hands of Massinissa, and the city being much weakened by it, they began to be apprehensive of the king himself, who was still near them with a large army, and also of the Romans, who were always harboring ill-will toward them and would make the affairs of Massinissa an excuse for it. They were not wrong in either particular. The Romans, when they learned the foregoing facts, straightway began to collect an army throughout all Italy, not telling what it was intended for, but in order, they said, to have it ready for emergencies. The Carthaginians, thinking to put an end to the excuse, condemned Hasdrubal, who had conducted the campaign against Massinissa, and Carthalo, the boëtharch, and any others who were concerned in the matter, to death, putting the whole blame of the war upon them. They sent ambassadors to Rome to complain of Massinissa, and at the same time to accuse their own citizens of taking up arms against him too hastily and rashly, and of furnishing an occasion for an imputation of hostility on the part of their city. When one of the senators asked the ambassadors why they did not condemn their officers at the beginning of the war instead of waiting till they were beaten, and why they did not send their embassy before, instead of postponing it till now, they could not give any answer. The Senate, which had previously resolved upon war and was only seeking some petty excuse, answered that the defense offered by the Carthaginians was not satisfactory. The latter, much disturbed, asked again, if they had done wrong, how they could atone for it. The answer was given in a word: "You must make it right with the Roman people." When they inquired among themselves what would make it right, some thought that the Romans would like to have something added to the pecuniary fine imposed by Scipio; others, that the disputed territory should be given up to Massinissa. Being at a loss what to do they sent another embassy to Rome, and asked to know exactly what they should do to make it right. The Romans replied that the Carthaginians knew perfectly well what was necessary, and having given this answer dismissed them.

source

Of course, one can certainly argue that the terms of the treaty that Carthage violated were far too harsh, and Carthage did not truly understand exactly what it meant when they signed it; Carthage believed that once they had paid their debts they were free of the rest of the treaty, but to Rome their subjugation was permanent. This misunderstanding of the treaty between the two sides only exacerbated the problem.

Edit: Wrong historian