From 1299, the newly founded Turkic state of the Ottomans had been slowly but surely capturing territory from the Byzantine Greeks. The loss of Nicaea was the beginning of a series of Ottoman expansion that lead to final dissolution of the Byzantine empire and its scattered Greek successor states.
Following the Byzantine defeat at Nicaea in 1331, the loss of Nicomedia was only a matter of time for the Byzantines. The Byzantine emperor attempted to bribe the Ottoman leader Orkhan, but in 1337, Nicomedia was attacked and fell to the Ottomans. The Byzantine empire did not recover from this defeat; the last Anatolian stronghold of Byzantium had fallen, except Philadelphia, was surrounded by the Germiyanids till 1396.
Following the loss of Nicomedia, the situation of the Byzantine empire remained untenable. Unlike the Byzantine empire at 1096, the Byzantine empire now possessed very little land, save a few cities in the peloponese. With its Serbian and Bolgarian neighbours pressing against its frontiers from the west and the Ottomans dismantling their hold on the east, the double-headed eagle of Constantinople was now truly looking in both directions at danger.
See also 
- R.G. Grant, Battle: A Visual Journey Through 5,000 Years of Combat, Dorling Kindersley Publishers Ltd, 2005. ISBN 0-7566-1360-4