In our live session on Saturday, we discussed the use of 'it' for emphasis', for example:
It was the Spaniards who introduced the Royal monopoly on salt.
Notice that 'was' is always singular because 'was' refers to 'it' ['it were* the Spaniards' is not possible].
'It' is often known as 'dummy it' because it does not refer to anything else in the sentence.
This 'dummy it' is often used in Listening and Reading texts, and it can be used to signal or emphasise the answer.
For example
Can you find some more examples?