SPOILER ALERT. In case you haven't finished the play, here's what goes down at the end:
1) King John gets poisoned by some crazy monk we've never heard of (offstage): Hmm. This is just weird, because it comes out of nowhere. We know King John has had his differences with the Catholic Church, but Shakespeare doesn't exactly prepare us for this, especially since John and the Pope make up in Act 5, Scene 1. Plus, we never even see this monk.
2) While King John is dying an agonizing death, all his enemies suddenly stop threatening him: While John's busy dying, the invading French forces just up and decide to go back to France and leave England alone, supposedly because Pandolf cut them a deal. Also, the rebellious English noblemen decide to be obedient to their king again (5.4.50-62). Um, okay, Shakespeare.
3) Shakespeare whips King John's son Henry out of a magic hat so he can become King Henry III when John dies: Oh, and did we mention that we never even hear about John's son Henry until Act 5, Scene 6, when his old man is dying?
Okay. The ending of King John is pretty random. Is this just a case of bad writing and thin plotting? (Some audiences and literary critics think so.) Or is there something else going on? Could all of these random turns of events actually mean something? Is this Shakespeare's way of saying, "Hey, sometimes life is unpredictable"? Well, it sure seems that way to us.
What's interesting is that Shakespeare's other history plays (especially Richard II; Henry IV, Part 1; Henry IV, Part 2; and Henry V) play with the idea that that English history unfolds according to God's divine plan, and that everything happens for a reason. Elizabethan audiences really ate that kind of thing up.
Now, even in those plays, Shakespeare seems kind of ambivalent about the whole thing: if you look carefully, you'll see that he seems pretty skeptical about all these political goings on. In King John, though, nothing really seems to happen for a reason, and the events that shape the course of history are totally unpredictable. The fact that he's so skeptical here is maybe a sign that even though he was subtler about his skepticism in his later plays, that skepticism is still there.
It may be that no king escapes Shakespeare's critical pen totally unscathed.
The Bastard's Big Speech
The other thing you should pay attention to at the end is the Bastard's speech, which makes up the final lines of the play. Here's a snippet:
This England never did nor never shall
Lie at the proud foot of a conqueror
But when it first did help to wound itself.
[...]
Naught shall make us rue,
If England to itself do rest but true. (5.7.118-120; 123-124)
Translation: England is awesome, and it's never going to be defeated by some foreign power... as long as the English people can stick together. This patriotic speech has a clear political message that wouldn't have been lost on Shakespeare's original audience. After all, England had just managed to fend off the Spanish Armada only a few years before King John was first performed.
Well, that's great and all, but what does it mean that this speech is coming from the mouth of the Bastard—not only a fictional character, but an illegitimate one at that? Are we supposed to believe this? Question it? Write it off?
Oh, Shakespeare, you're a tricky one.