The book on the Macedonian Wars belongs to the less preserved parts, but fortunately, we have access to Appian's sources Polybius or Livy.
The translation was made by Horace White; notes by Jona Lendering.
The Entr'Acte (Cont'd)
 [From the Suda] Philip utterly destroyed all forces that sailed against him, lest the Romans should say that the Macedonian power was weakening.
Outbreak of the Third Macedonian War
 [From Constantine Porphyrogenitus, The Embassies] The Romans were suspicious of Perseus (the son of Philip) on account of his rapidly growing power, and they were especially disturbed by his nearness to the Greeks and their friendship for him, due to hatred of the Romans, which the Roman generals had caused.note[172 BCE.] Afterward the ambassadors, who were sent to the Bastarnae, reported that they had observed that Macedonia was strongly fortified and had abundant war material, and that its young men were well drilled; and these things also disturbed the Romans.
When Perseus perceived this he sent other ambassadors to allay the suspicion. At this time also Eumenes, king of that part of Asia lying about Pergamon, fearing Perseus on account of his own former enmity to Philip, came to Rome and accused him publicly before the Senate, saying that he had always been hostile to the Romans; that he had killed his brother for being friendly to them; that he had aided Philip in collecting material for war against them, which material, when he became king, he did not desist from collecting, but added much more to it; that he was conciliating the Greeks in every possible way and furnishing military aid to the Byzantines, the Aetolians, and the Boeotians; that he had possessed himself of the great stronghold of Thrace and had stirred up dissensions among the Thessalians and the Perrhaebi when they wanted to send an embassy to Rome.
 [From Constantine Porphyrogenitus, The Embassies] "And of your two friends and allies," he said, "he drove Abrupolis out of his kingdom and conspired to kill Arthetaurus, the Illyrian chief, and gave shelter to his murderers."
Eumenes also slandered him on account of his marriages, both of which were with royal families, and for his bridal processions escorted by the whole fleet of Rhodes. He even made his industry a crime and his sobriety of life (being so young), and his being beloved and praised by so many in so short a time. Of the things that could excite their jealousy, envy, and fear even more strongly than direct accusations, Eumenes omitted nothing, and he urged the Senate to beware of a youthful enemy so highly esteemed and so near to them.
 [From Constantine Porphyrogenitus, The Embassies] The Senate, in fact, did not like to have on their flank a sober-minded, laborious, and popular king, an hereditary enemy to themselves, attaining eminence so suddenly. So, making a pretended accusation of the things alleged by Eumenes, they decided to make war against Perseus, but kept the matter a secret among themselves. When Harpalus, who had been sent by Perseus to answer the charge of Eumenes, and a certain ambassador of the Rhodians, desired to discuss the matter in the presence of Eumenes, who was still there, they were not admitted; but after his departure they were received. These, being angry at such treatment, and using too much freedom of speech, exasperated still more the Romans, who were already meditating war against Perseus and the Rhodians. Many senators, however, blamed Eumenes for causing so great a war on account of his own private grudges and fears, and the Rhodians refused to receive only his among all the representatives of the kings sent to their festival of the sun.
 [From Constantine Porphyrogenitus, The Embassies] When Eumenes was returning to Asia, he went up from Cirrha to Delphi to sacrifice, and there four men, hiding behind a wall, made an attempt upon his life. Other causes besides this were advanced by the Romans for a war against Perseus, although it had not yet been decreed, and ambassadors were sent to the allied kings, Eumenes, Antiochus, Ariarathes, Massinissa, and Ptolemy of Egypt, also to Greece Thessaly, Epirus, Acarnania, and to such of the islands as they could perhaps draw to their side. This specially troubled the Greeks, some because fond of Perseus as a Philhellene, and some because compelled to enter into agreement with the Romans.