I've mentioned before that cutting lines or scenes from a Shakespeare text is a mistake. Today, I'd like to turn your attention to a scene from Hamlet that is, unfortunately, frequently excised: the scene between the player king and his queen during the play-within-the-play scene. In it, the player king is trying to tell his wife that he doesn't have long to live, and that he is fine with the fact that she'll remarry after his death. The queen interjects that she has no plans to do so, and that in fact those who do are not doing it for love, but for other reasons. Then the player king has a remarkable speech that reveals one of the play's deepest themes: the fact that alliances form and break with time and with necessity. And that human beings are, in essence, survival-machines that will do what is needed when it is needed. Therefore, promises (like the queen's) may be made in an emotional way, but when new emotions arise, they will (and perhaps should) be forgotten. Here is the excerpt (which is purposely written in an older style of verse):

Player Queen

The instances that second marriage move

Are base respects of thrift, but none of love:

A second time I kill my husband dead,

When second husband kisses me in bed.

Player King

I do believe you think what now you speak;

But what we do determine oft we break.

Purpose is but the slave to memory,

Of violent birth, but poor validity;

Which now, like fruit unripe, sticks on the tree;

But fall, unshaken, when they mellow be.

Most necessary 'tis that we forget

To pay ourselves what to ourselves is debt:

What to ourselves in passion we propose,

The passion ending, doth the purpose lose.

The violence of either grief or joy

Their own enactures with themselves destroy:

Where joy most revels, grief doth most lament;

Grief joys, joy grieves, on slender accident.

This world is not for aye, nor 'tis not strange

That even our loves should with our fortunes change;

For 'tis a question left us yet to prove,

Whether love lead fortune, or else fortune love.

The great man down, you mark his favourite flies;

The poor advanced makes friends of enemies.

And hitherto doth love on fortune tend;

For who not needs shall never lack a friend,

And who in want a hollow friend doth try,

Directly seasons him his enemy.

But, orderly to end where I begun,

Our wills and fates do so contrary run

That our devices still are overthrown;

Our thoughts are ours, their ends none of our own:

So think thou wilt no second husband wed;

But die thy thoughts when thy first lord is dead.

There are books that contain historical maps of Europe (for example) which show how friendly nations have become enemies, and vice versa, many times over. Have a look at one while keeping this passage in mind.