Whatsapp has connected people in such an efficient way that it is pretty difficult for a regular user to imagine the loss of conversations or other data. Loss of chats is mainly due to changing phone or failure of restoring messages. Chats can be recovered in just few steps if one changes their phone. But in case there is a failure in setting up backup , chats will be lost.
Connect your old phone to laptop or computer.Find the whatsapp folder in file manager and move it to laptop.
Move it to your laptop or computer.
Eject the previous phone and connect the new one.
Move the folder to the new phone.
Eject the new phone.
Re-install whatsapp on new phone and verify your previous registered account.
There would be a message of back up found.
Using Google Drive
Go to settings>>chats.
Choose chat backup.
Click on back up. Your chat will be backed up to google drive.
Re install whatsapp and verify the previous number.
Click on restore.
Your chats would be restored.