Reference Books: 

https://www.encyclopedia.com/  

https://www.britannica.com/  

https://www.worldhistory.org/  

https://www.tumblemobile.com

 https://www.oxfordowl.co.uk/  

https://www.starfall.com

https://www.biographyonline.net/  

https://www.history.com

https://onlineessays.com/  

https://www.goodreads.com