A combined spice, mostly dried and ground vegetables, lots of salt and then MSG. The MSG addiction has spread across the borders, so many gastarbajters were buying it by the kilo when they visited home, and for a couple of decades it was the most popular item to smuggle into the neighboring countries of eastern bloc (Hungary, Romania, Bulgaria, even USSR). It is still made in Croatia and exported to many countries in the region, and some quantities make it across the ocean - if you know where to look, you'll find it in any larger american city. Several lookalikes (some even better, with more vegetables and less salt, some even without MSG) are made in Serbia now, but there are many who swear by the old Vegeta.