To talk about the future seen from the past we use the past tenses of the verb forms we would usually use to talk about the future.
Compare:
We didn’t know our travels were going to change our lives.
We believe our travels are going to change our lives.
In the first sentence we know the result, whereas in the second we are predicting the result.
In the first sentence we are talking about the future seen from a point in the past. In the second sentence we are talking about the future seen from now.
Compare:
The future seen from now —> The future seen from the past
am/is/are going to + infinitive —> was/were going to + infinitive
eg. … our travels are going to change our lives. —> …our travels were going to change our lives.
will + infinitive —> would + infinitive
eg. … this successful student will go on to become… —> … this successful student would go on to become…
is/are supposed to + infinitive —> was/were supposed to + infinitive
eg. … this new technology is supposed to save people time. —> … this new technology was supposed to save people time.
am/is/are about to + infinitive —> was/were to + infinitive
eg. … they are to discover… —> … they were to discover…