The excerpt changes tenses because it's talking about things at different times. The first paragraph describes completed actions which took place in the past, hence the use of past tense. The second uses the present because it's talking about things at the current time or the recent past. The third begins by talking about the past, then proceeds to discuss the current state.
Think of the first paragraph like a big quotation. It's not describing any specific actual events - indeed, the second paragraph says that the first could describe several places - just some generic history. Because it's talking about history, it's in the past tense.
It sounds in the second paragraph is talking about the first paragraph. This is in the present because you're currently reading the article. Its words sound a certain way at the time you read them. Incidentally, I find this:
But this is also, and originally, Algeria, a quarter of a century earlier—the first major political crisis in the age of modern Islamism.
somewhat confusing; specifically, the aside about Algeria. I get the meaning (I think!), but I think the remark should be expanded a bit, and probably in the past tense.
The third paragraph opens by discussing completed actions in the past:
A flurry of freedom in the late 1980s gave way...
This first sentence sets the stage with some historical context. After giving us a bit information about the past, it goes on to describe the present state of affairs, appropriately shifting to the present tense to do so:
Today the country’s citizens remain powerless spectators...
Past, present and future match up with the times being described. Very generally speaking, you should work towards maintaining a single tense in your writing, especially if you aren't comfortable with the fine details of changing them. But there are plenty of reasons to change tenses. For example:
- Simple descriptions of events, as commonly seen in news, should be in the relevant tense (past events in past tense, etc).
- Literary foreshadowing might call for future tense: he gazed over his shoulder at her. He would never do so again.
- Dialogue written as spoken or thought by persons involved should be tensed as it normally would when speaking; e.g. she said, "I will go to the store tomorrow."
Given I am X, what's valid for X is in almost all cases is the following:
an adjective (I am hot, I am third, I am ready)
a noun or pronoun (I am a cat, I am a worker, I am him, I am George)
a verb's present participle form, these always end in -ing (I am walking ..., I am envying ...)
a verb's past participle form if it makes sense to express a state and can also work as an adjective (I am destroyed, I am surprised)
rarely, a preposition (I am of the tribe, I am to lead my group)
any of the above with an adverb in front, (e.g. I am very X)
Adverbs can appear between I and am, like really, definitely, etc.
What X can't never be is the plain form of a verb.
So you can say I am walking but never I am walk.
You can say I am to walk but not I am walk.
You can say I am cooking hamburgers or I cook hamburgers but never I am cook hamburgers.
You also are required to express am in all the above situations. Am is not optional, but it's often said in the contracted form I'm.
Best Answer
As J.R. says, singular or plural deserve will work equally well. The bare sentence may be parsed as either:
There is, however, an overriding consideration. This line is a quotation from a poem by John Dryden, Alexander's Feast; or, the Power of Music.
Dryden wrote it singular, with ‘the brave’ referring specifically to Alexander and ‘the fair’ referring specifically to Thais.
ADDED:
In present-day English we no longer use the ADJECTIVE to refer to a single person except in epithets (e.g. Alexander the Great), only for classes of people. The singular therefore sounds odd to anyone who does not know the source of the line—which is probably 99% of the people who use it.