High corporate taxes + global taxation of profits. For example, any profit coming from lower taxed subsidiary (i.e. a dividend) will be taxed at the difference between the local rate and US corporate tax rate. So if you pay 20% in the UK, you will have to pay an additional 15% (35%-20%) in US tax.<p>Second, the US is very aggressive when it comes to withholding taxes (FATCA and all) - if you’re a shareholder living in a country without a decent tax treaty with the US, you’ll lose an extra 30% on any dividend you declare, unless you include intermediary structures such as holding companies etc<p>Now, some of these might not matter that much to a startup since they aren’t making a profit anyway. But if you build something profitable it will be relevant for an acquirer. If things are set up properly to pay less tax, they will pay more for your company.