The Quran promotes monogamy as the basis for normal relationships, allowing polygamy only in exceptional circumstances to care for orphans. Polygamy is permitted to marry the mothers of fatherless children or widows after war to provide for them, with a maximum of four wives. However, the Quran emphasizes being fair and just to all wives, and that monogamy is preferred if fairness cannot be guaranteed in a polygamous marriage. It was revealed in a society where polygamy was common but sets restrictions to reduce it.

3. Some think that Muslim men can have multiple wives if they
desire to and that Islam and The Quran promotes polygamy.
The Quran is very clear on this subject, that monogamy is the
basis for normal relationships, while polygamy is only allowed in
cases involving marrying the mothers of orphans so that the
orphans are taken care of. A maximum of four wives are allowed
in such cases. For example, in the aftermath of war, it is likely that
many men would have lost their lives, resulting in many widows
with fatherless children, thus The Quran allows an exception in
these cases so that the needs of the wider community can be met:

4. Give the orphans* their money; do not replace the good with
the bad, and do not consume their money to your money, for
truly it is a great sin! And if you fear that you cannot be just to
the orphans, then you may marry those who are agreeable to
you of the women: two, and three, and four. But if you fear you
will not be fair, then only one**, or to whom you are committed
to by oath. This is best that you do not face financial hardship.
[4:3]
*the Arabic word for "orphans" is "yatama" and specifically
means children who are fatherless.
** note the emphasis on one wife, i.e. monogamy.

5. Again, the subject of polygamy is addressed in the
context of orphans:
They ask you for divine instruction concerning
women. Say, "God instructs you regarding them, as
has been recited for you in the book about the mother
of orphans who you want to marry without giving
them what has been ordained/written for them, as
well as the powerless children, and your duty to treat
orphans with equity. Whatever good you do, God has
full knowledge of it. [4:127]

6. The above verse has been commonly mistranslated to justify
marrying orphan girls rather than marrying their widow
mothers. The Arabic plural pronoun in this verse is the
female form, "allatee" (not the male form "allazyna"), and it
can only refer to the women just referenced, not to the
orphans. This is because in Arabic the word "yatama"
(orphans) is grammatically male in gender. The beginning of
the verse also tells us the subject of the verse, it is about the
women. That is why it is important to remember all
translations are imperfect, and to seek knowledge and verify
information for oneself [17:36].

7. Again, The Quran shows a preference
for monogamy in the following verse:
And marry the single from among
you as well as the good from among
your male and female servants. If they
are poor, then God will grant them
from His grace. God is
Encompassing, Knowledgeable.

8. To summarise, The Quran was revealed to a
society where polygamy was commonplace
and men could have many wives (e.g. more
than four for example). By setting an upper
limit, citing a moral restriction on polygamy
and limiting the situations in which it is
allowed would result in reducing polygamy
significantly.