When we construct a sentence, we choose (consciously or not) what information to emphasise. By prioritising a particular part of what we say, we can draw attention to certain information and/or choose to make other pieces of information less salient.
There are three main ways of prioritising certain elements in a piece of language. Perhaps the easiest to recognise is the information structure of sentences. In English, new and important information tends to be placed at the end of a sentence. If we take a sentence like 'The coalition government cut public spending', we can see that it is the issue of public spending that is the salient information here: the fact that the coalition government is involved is 'got out of the way' early on, in subject position at the start of the sentence, with the predicate ('cut') and the object ('public spending') giving the 'meaty' part of the information - what it is that has happened.
The salience of final clause elements is also of relevance in the transformation that can make an active sentence passive: here, the verb is made passive, so that we get the sentence 'Public spending was cut (by the coalition government)'. Now it is the process of the cutting of public spending that is the focus of the sentence, with the agent of this cutting being made into an optional adverbial which could be elided altogether. Note that such an elision would suit a writer who might want to draw attention away from who is responsible for the cutting of spending.
Finally, subordination allows writers and speakers to 'tuck away' certain bits of information at a low level of sentence structure, where it will be less prominent. This can be helpful to writers or speakers who want to present one side of a story as being more important than another, e.g. 'Barack Obama offered the American people hope, while Mitt Romney offered nothing new to voters'. Here, Mitt Romney's relegation to a supplemental subordinate clause makes his contribution appear less significant than Barack Obama's. Subordination also allows writers and speakers to package certain information as 'given', by placing it within noun phrases. For example, a commentator wanting to present cuts to public spending as unquestionably a bad thing might relate how 'The government's planned public spending cuts, which will harm all but the most privileged, are being presented as the only viable option'. Here, the relative clause beginning at 'which' allows the writer to make a potentially contentious point about the public spending cuts without placing it in its own proposition, making it difficult to argue against.
A famous passive structure frequently used in political language is 'mistakes were made'. By stating simply that 'mistakes were made', the speaker acknowledges that something went wrong, but neglects to mention an actor who was responsible for that something. Variations on the phrase were used in a 2005 interview between Tim Russert of NBC News and Republican Senator John McCain regarding the second Iraq war. In the interview, McCain acknowledged that "one of the many mistakes that have been made is to inflate the expectations of the American people... that this was going to be some kind of day at the beach", and that "Serious mistakes are made in every war. Serious mistakes were made in this one". Hearers can often be frustrated by such passivisation: by omitting the subject position in which they or a body they are associated with might be placed, the speaker ends up sounding less contrite than their audience might like them to.
"Under the situation where a war may break out at any moment, there is no need to keep north-south military communications which were laid between the militaries of both sides."
In this example, the long adverbial phrase - beginning with 'under' - has been placed at thr front of the sentence. This serves to place added attention on the adverbial, which - notably - contains the warning that "war may break out at any moment". Look out for examples of language in conflict where adverbial or subordinate clauses appear to be being used carefully for effect.
'Prioritizing' in Jeffries' book guides the reader through the different ways in which sentences can be structured, and looks at the potential for ideological significance:
Jeffries, Lesley. 2010. Critical Stylistics: The Power of English. Hampshire: Palgrave, 77-92.