One remarkable advantage for the US economy is the large size of its internal market. US firms can make investments in new goods and services knowing that they can potentially sell, with only a few limitations rooted in state laws, to a large number of customers across a broad area.

Indeed, the openness of the US internal market is rooted in the US Constitution. Article 1, Section 8, lists the powers of Congress, and the third clause gives Congress the power to “regulate Commerce … among the several States.” By giving that power to Congress and the federal government, the Constitution blocked states from setting up barriers to trade with each other–for example, although US states can pass laws that may create indirect costs for companies buying and selling across stated, they can’t impose tariffs or quotas on goods and services imported from other US states.

A primary goal in creating the European Union was to replicate this “single market,” and thus to give European firms the incentives for innovation, investment, and expansion that result from wide-open access to a large internal market. But according to the IMF Regional Economic Outlook report on “Europe: A Recovery Short of Europe’s Full Potential,” the EU “single market” project has a long way to go (October 2024). Here’s a sample (references to text “boxes” have been cut:

Europe’s productivity gap with the global frontier can be traced back to a more limited market size, capital market constraints, skilled labor shortages, and stalled structural reforms. Firm-data analysis shows that Europe’s segmented good and services markets are keeping businesses from becoming larger, spending more on R&D, and exploiting economies of scale. Moreover, fragmented capital markets mean that firms do not draw enough on equity financing. As a result, business dynamics are dampened especially in the services sector where start-ups tend to operate with large intangible capital. …

There is widespread agreement on the sources of Europe’s growth weakness. Recently released expert studies (Letta 2024; Draghi 2024) come to a similar conclusion that Europe’s low productivity is related to lack of market depth and scale. Both reports link Europe’s lack of competitiveness to Europe’s incomplete single market in the trade of goods, services, and factors of production (capital, labor). Remaining barriers are considered to be still substantial and have resulted in less investment and innovation than necessary to accelerate growth and productivity to levels seen in other advanced regions.

A deeper and larger single market offers the potential for a resurgence in productivity growth. European integration delivered tangible growth benefits in the past and could do so again. Following the two EU enlargement waves in 1995 and 2004, EU member countries began trading more with each other (Figure 15, panel 1). As a consequence, in the decade following accession, regions in new member states saw on average GDP per capita rise by more than 30 percent relative to comparable non-accession regions and existing member states gained too.

It is important to note that regions within Europe that were better integrated through value chains and transport networks registered higher gains. However, value chain integration has stalled since the last decade … and substantial barriers to goods and trade flows remain … New IMF analysis finds that in 2020 trade costs within Europe were equivalent to a sizable ad-valorem tariff of 44 percent for the average manufacturing sector compared to 15 percent between US states, and as high as 110 percent in the case of services sectors …

Here is a figure to which the IMF is referring. The darker blue line shows intra-EU trade in goods; the lighter blue line shows intra-EU trade in services. As you can see, intra-EU trade in goods had risen substantially up to about 2008, but has only crept a little further since. Intra-EU trade in services remains less than 10% of their value, 30 years after the birth of the “single market” initiative back in 1993.

Again, the IMF estimates that remaining barriers to trade within the countries of the EU are equivalent to a 44% tariff on trade in goods, and a 110% tariff on trade in services. These high tariffs are bad for economic growth in Europe, just as similar state-level tariffs would be bad for US growth. Of course, the underlying economic reasoning also explains why a global outbreak of tariffs would be disadvantageous for both US and global growth.