Article: The Czech people gained widespread national pride during the mid-eighteenth century, inspired by the Age of Enlightenment a half-century earlier. Czech historians began to emphasize their people's accomplishments from the fifteenth through the seventeenth centuries, rebelling against the Counter-Reformation (which had denigrated Czech and other non-Latin languages). Czech philologists studied sixteenth-century texts, advocating the return of the language to high culture. This period is known as the Czech National Revival (or Renascence).

Now answer this question: What did Czech historians emphasize about their countrymen?
accomplishments
The first two paragraphs of the article state that Czech historians emphasized their people's accomplishments during "the fifteenth through the seventeenth centuries". 
So, it can be inferred that this is what they wanted to emphasize about their countrymen..