Different countries have different currencies based on locations, natural resources, and some other aspects. This differences can be barriers between those countries to do trading processes. Moreover, considering the scale of globalisation make the countries need each others. To address this problem, some people say that single world currency is needed to remove the barrier. I disagree with the opinion because that means the money is maintained by one country. This monopoly can benefit certain groups and different exchange rates for each currency can lead to problems.
First, using one kind of money may lead to monopoly of certain groups. Those groups can rule the world by increase or decrease the price of properties. This can happen if transactions are private and handled by banks. However, turning the transaction histories into transparent will solve the distrust problems. For instance, cryptocurrencies adapt this method to earn people’s trust. Everyone can see the whole transaction histories to make sure all transactions are fair.
Second, centralizing the currency means that all countries must exchange their currencies to the agreed one. By considering that every country has a different value of currency compared to the agreed one, some nations may obtain less exchanged value than others. That will trigger inflation in several countries, making poor countries become poorer and otherwise. For example, when world accept Dollar as main currency, the developed country like Indonesia will have a big change on the price of all things, since Rupiah has low exchaged value on Dollar.
In conclusion, converting the wealthies of all countries into the one main currency will create some problems like distrust and inflation. Thus, it is better to keep the currency like this time.