It is not often that specific international tax proposals are included in national level coalition agreements but it seems Belgium is so intent on promoting the idea of a global minimum tax rate that the political parties who form the Vivaldi Coalition have committed themselves to each other to promote it within the OECD and to further the chances of a global digital services tax.
Expect the EU to lead the charge as normal in such matters. Tax sovereignty within the EU is now a much less debated topic as the UK departs, but one is required to consider what does tax sovereignty amount to if the global system disallows expenses paid to entities taxed below a certain level? Will a country that just simply does not need to tax at a rate higher than the minimum rate set by the OECD (of which the vast majority of jurisdictions are not full members) become an international pariah merely for taxing no more than it requires to look after the interests and well being of its residents?
Alternatively would a jurisdiction ever reduce its headline rate below the agreed minimum threshold? Tax is complex, some jurisdictions have low headline rates and very simple taxation systems, some (more like the US model, for example) have high headline rates and many special treatments for specific areas. It is perfectly possible to have lower headline rates and collect much more in tax if you design your system differently. This proposal will possibly have the effect of smoothing those differences and limit the scope for national parliaments to design their taxation systems in the way they see fit.
The ultimate agreement will undoubtedly preserve the outward form of tax sovereignty I am sure but the litmus test will be how many jurisdictions feel obliged to inflate their tax rates to meet the minimum requirement, and whether we see a coming together of tax system design in the coming decades.