Hey there!
Orson Welles firstly made it into a present and more modern tense, making it seem like it was actually happening at that current moment.
Additionally, he also made it sound like news briefs, making the invasion by Martians of New Jersey sound even more realistic.
All of these methods in total added up to millions of people across America in sudden shock, wondering if they were safe from these violent and peculiar Martians.
Hope this helps!