The piety and virtues of Vladimir (no comma required!) compelled many sovereigns to send ambassadors to him: namely, from Stephen I, King of Hungary, Boleslav III, King of Bohemia, Boleslav I, King of Poland, Pope Sylvester II…
Nicely put: piety and virtues compelled many sovereigns to send ambassadors. And then
Vladimir, having fortified his Realm with various strongholds and with the courage of the people he had enlightened, began to consider how he might establish peace among his children for all posterity, knowing that discord between brothers can bring about many misfortunes.