Sometimes the presence of a monarch is the only thing holding a country together. In Thailand, for example, the monarch's reign prevents the country from falling into civil strife.
In multiethnic countries like Belgium, the people are united insofar as they all support and remain loyal to their monarch.
This is despite having different views and sentiments about important social, political, legal, and economic matters. A monarch can also be a symbol of unity between diverse ethnic communities.
A sovereign also prevents conflict because allegiance is given to the monarch and not to any ethnic or tribal group. The Habsburg dynasty of Austria united a large country and enabled it to continue prospering until it split into smaller, mutually hostile groups, each one lacking in power after World War I.
If the former king of Afghanistan, Zahir Shah, who was admired by all Afghans, returned to kingship after the Taliban were overthrown in 2001, Afghanistan may have overcome the factionalism and conflict that arose between different aggressors more swiftly.
Most of today's monarchs do not rule the way ancient monarchs ruled. Their power is not absolute and is restricted and conditioned by constitutional structures.
Prime ministers and parliaments now influence their decisions and commands.
Today, their primary role is to unite, encourage, and influence as inspirational symbols without the troubles of ruling.