The historical evidence can be found from the historical sources. The historical sources can be divided into two categories which are the primary sources and secondary sources. Sometimes, primary sources were considered as first-hand sources while the secondary sources were considered as second-hand sources. In order words, primary sources were recorded by someone who actually knew, experienced or witnessed the whole thing including the beginning, development and ending; and the secondary sources are the primary sources that have been taken out one or more pieces of information by others who did not originally experience or witness how the thing was going on. An important relationship between primary and secondary resource is that the secondary sources were the interpretations and the analysis of primary sources.