What is happening in the world at any time has a HUGE effect on design. You need to look at what was happening during the time of your design era and analyses how those events affected your design era.
Use this flow diagram to help you to explain how these elements effect the design of the time and why.
In the elements column put 4 things that were happening in the world at the time of your design era.
In the second column put a little bit of information about those 4 things
In the third column, talk about how those things that happened affected design at the time.
In the last overview column, bring it all together in a summary
Possible sources for your information - use these as starting points and then do you own searches for information.