Pada tahun 215 BC, ia mengadakan [[:en:Macedonian–Carthaginian Treaty|perjanjian]] dengan [[Hannibal]], jenderal [[Karthago]] yang saat itu sedang menyerang Italia Romawi. Perjanjian mereka mendefinisikan lingkup operasi dan minat, tetapi hanya mencapai sedikit nilai bagi kedua belah pihak. Filipus menjadi sangat terlibat dalam membantu dan melindungi para sekutunya dari serangan orang [[Sparta]], Romawi dan sekutu-sekutu mereka.
[[Image:ThermoAitolias.jpg|thumb|right|Reruntuhan [[:en:Thermo, Greece|Thermo]] ibukota [[Liga Aitolia]], suatu kota yang direbut oleh tentara Filipus V.]]
Aliansi Romawi dengan [[Liga Aitolia]] pada tahun 211 SM secara efektif menetralisir keunggulan Filipus di daratan. Intervensi [[:en:Attalus I of Pergamum|Attalus I dari Pergamum]] pada pihak Romawi lebih membuka kelemahan posisi Filipus di Makedonia. Filipus mampu mengambil keuntungan mundurnya Attalus dari daratan Yunani pada tahun 207 SM, bersama dengan ketidakaktifan Romawi dan meningkatnya peranan [[Philopoimon]], [[strategos]] [[Liga Akhaia]]. Filipus dan tentaranya merebut [[:en:Thermo, Greece|Thermum]], pusat agamawi dan politik [[Aitolia]]. Tentaranya menghancurkan 2000 patung dan membawa pergi harta yang berlimpah termasuk sekitar 15000 [[perisai]] dan baju perang yang menghiasa [[:en:stoa|stoa]] orang Aitolia.<!-- Perisai-perisai itu merupakan perlengkapan perang yang diambil dari musuh-musuh orang Aitolia selama kemenangan-kemenangan mereka pada waktu lampau dan termasuk perisai-perisai orang [[Gaul]] yang menyerang Yunani pada abad ke-3 SM.<ref name=" Mackil 2013 ">{{cite book |title=Creating a Common Polity: Religion, Economy, and Politics in the Making of the Greek Koinon |last= Mackil|first= Emily |year= 2013 |publisher= University of California Press |isbn= 9780520953932|quote= When Philip V sacked Thermon in 218, Polybios tells us that his army hauled away some fifteen thousand shields that been laid up in the stoas. Although the number is surely exaggerated, Polybios’s report suggests that the Aitolians had decorated their stoas with armor taken from enemies, and [[Jean Bousquet]] is certainly correct to surmise that at least some of these were Gallic shields taken as booty in 279. Yet the dedication of shields taken from defeated enemies appears to have been a traditional privilege of the Aitolian strategos, and it would be misleading to assume that all or even most of the dedicated armor at Thermon was Gallic. |page= 214}}</ref> Filipus V mengambil sejumlah besar [[emas]] dan harta kemudian membakar hangus kuil-kuil dan bangunan-bangunan publik orang [[Aitolia]].<ref name=" Vandenberg 2007 ">{{cite book |title=Mysteries of the Oracles: The Last Secrets of Antiquity |last= Vandenberg |first= Philipp |year= 2007 |publisher= Tauris Parke Paperbacks |isbn=9781845114022 |quote= Philip V of Macedonia, with whom the Epirotes were in league, exacted terrible revenge for the Aetolian raid the following year. He razed Thermum, the national shrine of the Aetolians and the meeting-place of the Aetolian League, to the ground. Temples and public building were burned down and more than two thousand votive statues were smashed; only statues of the gods themselves were spared. The booty in money and gold was so vast that Philip was able to rebuild his sacred city of Dion at the foot of Olympus, and the Epirotes, the sacred precinct of Dodona, bigger and better than before.|page=37 }}</ref> Filipus mampu memaksa orang Aitolia untuk menerima syarat-syaratnya pada tahun 206 SM. Pada tahun berikkutnya ia mampu mengadakan [[:en:Peace of Phoenice|Perdamaian Fenise]] dengan Roma dan para sekutunya.
