Short answers, pulled from the story.
The word republic originates from the Latin phrase res publica, meaning public thing or people's thing, a concept that first emerged in ancient Rome to describe a state where political power rested with the public rather than a single ruler.
The Roman Republic lasted from the overthrow of the kings in 509 BC until the establishment of the Empire in 27 BC.
Arwad has been cited as one of the earliest known examples of a republic, in which the people, rather than a monarch, are described as sovereign.
The Icelandic Commonwealth was established in 930 AD by refugees from Norway who had fled the unification of that country under King Harald Fairhair.
On the 2nd of June 1946 the republican side won 54.3% of the vote and Italy officially became a republic, a day celebrated since as Festa della Repubblica.
Under the leadership of Sun Yat sen, the Republic of China was proclaimed on the 1st of January 1912.