This is the 3531st most frequent Russian word.
республику
The accusative form of "republic," meaning a type of government or state.
In this sentence, "республика" (translated as "republic") is in its accusative singular form "республику", used as the object of the preposition "о".
Я выучил много интересных фактов о этой республике.
I have learned many interesting facts about this republic.
Here, "республика" is also in the accusative singular form "республику", as it follows the preposition "по" and describes the location our travels took place.
Мы путешествовали по этой прекрасной республике.
We traveled through this beautiful republic.
In this example, "республика" as "республику" denotes a direct object of the verb "выбрали", showing the choice of a governing system.