The Roman Republic was a phase in history of the Ancient Roman Civilization. According to legend, the city of Rome was founded by Romulus in 753 BC. It was a kingdom until 510 BC, when the last King, Lucius Tarquinius Superbus was overthrown. With that date, the Roman Republic began.
The Roman Republic was a civilization ahead of its time and very advanced. The Roman people elected Consuls, who ruled for a short time. Some of the ideas of the Roman Republic are still used today.
The end of the republic is still a matter of dispute; different scholars will give different dates for it. Usually, the dates of the start of the First Triumvirate or the Second Triumvirate are given. (The Triumvirates were groups of three men who had much power)
The end of the republic is often said to be when Gaius Julius Caesar was appointed as dictator (single ruler) by the Roman Senate. This happened after a series of civil wars that lasted from about 49 BC to the year 44 BC.
Some people say the republic ended with the naval Battle of Actium between Marcus Antonius and Octavian. They both had been in the Second Triumvirate. It was fought on September 2, 31 BC. Octavian won. Later on, he was proclaimed Roman Emperor. The end date could also be when Octavian was given the title of the first Augustus. This was on January 16, 27 BC.
These are modern views though. In the view of the early emperors, the res publica (what is translated to Republic) still existed. It was simply "under their protection". They promised it would some day, maybe, be restored to its original form. This never happened, and so the beginning of the Roman Empire was the end of the Roman Republic.
The Republic got most of its wealth from trading and taxation. The Republic had few enemies but it was constantly on war with the Gauls, who were conquered by Caesar later. The Punic Wars against Carthage were fought all over the Mediterranean coasts, mainly because of Sicily and trade disputes. The third enemy being the Germanic tribes or simply barbarians (uncivilized people).
The Republic suffered many disasters including Spartacus (the leader of a slave revolt) Spartacus defeated one consul's army before being captured, the Republic suffered at the hands of Hannibal, who after crossing the Alps defeated the Roman Army at Cannae and many other battles which saw Rome with a great fear of being destroyed by Hannibal.