During The Time Of Mahabharat War What About Other Continents People Other Then Asia Like America.

How is the authenticity of Ramayana and Mahabharata justified?

India was not called or considered as whole world, instead it was referred as “Jambu Dweep” or “Jambu Island”. Also Mahabharat was fought between the rulers all around the world, including europe and Asia.This is the rough interpretation of world map given by Ved Vyasa. It explains that earth has two Hemispheres. One hemisphere has ground in the shape of rabbit and the other in shape of two peepal leaves.So yeah they pretty much knew it.

What was the world like during Lord Rama's period? Was India the only nation in the world?

There were dinosaurs, unicorns and dragons. Surya dev used to come every morning riding on his 7 horse chariot. As it was Satya yuga, people never told lies. There was not a nation called 'India' or 'Bharat' or 'Hindustan'. But there were several nations like Ayodhya, Lanka et al. South Indian and Sri Lankan people who were of Dravida race, had curly hair, dark skin and worshipped Shiva, were called as Rakshasas or Asuras (Ravan being the one of them). Tribals in Dandakaranya (Today's  Chhattisgadh, Vidharbha, Western Odisha and some northern Telangana districts, in short India's 'Red Corridor') who used to apply color on their faces were called 'monkeys' (vanaras) by the North Indian Aryan city people (this trend is seen even today in urban people of India).There were aeroplanes like Pushphak which were available only to kings and ran not on fuel, but on powerful mantras.Although, some special characters like Hanumana, Jatayu and Narad had the cheat codes to fly without vimanas.There used to be a herbal mountain called 'Sanjivani' near Himalaya. But now it's relocated to Sri Lanka. Baba Ramdev is negotiating to bring it back for the development of Ayurveda in India.There was positive energy everywhere. Measuring at about thousands of kilojoules/square bigha.Women were happy. Four women had to share a husband, so their worries were only a quarter. Although, they couldn't go outside without permission of their hubbies. But a simple fire test (agni pariksha) was enough to prove their purity (Burn impure bitches!). There was a series of limestone rocks from southern tip of Tamilnadu to Jafna island of Sri Lanka. Vanaras (tribals) effortfully wrote the name of Rama on those rocks as so they could find the path on the way back.Rama won the war against Ravana and returned. When the Vanaras and people of Ayodhya came to know that Hanuman had visited Seeta in Ashokvana and she could return with him without risking a war; people got furious and banished Ram Lakshman and Seeta for causing unnecessary war and costing many precious monkey lives. Seeta returned where she came from - the underground. Finding no place to go, Ram and Lakshman took a long underwater cruise on the river Sharayu to never return back.People of Ayodhya celebrated this day by hoisting red flags on their homes. This day is still celebrated today in Maharashtra as 'Gudhipadwa'.

What were the other civilizations doing during the period of Mahabharat?

To the west of Sindhu, were the people of Gandhara (Afghanistan) and Persia (Iran). Their princesses Gandhari and Madri were married into the Kuru clan.Tibet was inhabited by the people of Yaksha, Kinner and the Gandharva civilizations. Many of them play a role in the Mahabharata. Beyond Tibet the Chinese civilization was coming up.Then there was the Naga civilization. Many Nagas including Takshak play a role in the Mahabharata.The Egyptian and Assyrian (Mesopotamia, Iraq) civilizations were developing too.In Britain, during the times of Mahabharata, the Druid people were building the Stonehenge. While the Nordic tribes populated the Scandinavian countries.*Note. I consider Mahabharata war to have been fought somewhere near 3100 BCE.