Michael's reign included the usual wins and losses on the Arab front. However, despite Leo V's treaty with the Bulgarians of 815, the empire was once again at war in the Balkans in 855. However the subsequent conversion of the Bulgarians to Christianity and the peace of 864 brought a long lasting lull in the Bulgarian wars. A new threat emerged further north in 860 with the appearance of the Kievan Rus' and subsequent Rus'–Byzantine wars of 860.