The evolution of the Greek economy during the 19th century (a period that transformed a large part of the world because of the Industrial Revolution) has been little researched. Recent research from 2006 examines the gradual development of industry and further development of shipping in a predominantly agricultural economy, calculating an average rate of per capita GDP growth between 1833 and 1911 that was only slightly lower than that of the other Western European nations. Industrial activity, (including heavy industry like shipbuilding) was evident, mainly in Ermoupolis and Piraeus. Nonetheless, Greece faced economic hardships and defaulted on its external loans in 1826, 1843, 1860 and 1894.
Try to answer this question if possible (otherwise reply "unanswerable"): What did Greece do in 1826, 1843, 1860 and 1894?
defaulted on its external loans