Complex sentence: The export of metal ores and metalwork (mainly silver, copper and lead) formed the backbone of the Bosnian economy, and these goods were transported over the Dinaric Alps to the seaside, from where they were bought chiefly by the Republics of Ragusa and Venice.
Split into simpler sentences: The export of metal ores and metalwork (mainly silver, copper and lead) formed the backbone of the Bosnian economy. These goods were transported over the Dinaric Alps to the seaside, where they were bought chiefly by the Republics of Ragusa and Venice.