In The Divided West, Habermas writes as a European intellectual staking out a path forward in the post-9/11 world, not in the technical language of his political philosophy and epistemology. He lays out the theoretical foundation of an alternative to US unilateralism and theocratic totalitarianism.
Habermas writes eloquently of the pedigree of the Kantian vector of cosmopolitan thought and its evolutes, and draws on these traditions to elucidate a concept of international law based on reason and consensus. It's hard to be unmoved by the moral worth of investment in the rational internationalism of the European Enlightenment. What serious alternative do we have, assuming one does not accept the odious exceptionalism that pervades the US policy of preemptive adventurism, which draws legitimacy solely from the power to wage war?
But, as is so often the case, the devil is in the details. Peering outside the walls of theory, we can see that in the decade following the 9/11 shift in geopolitics, Europe has done a poor job of investing the necessary human, military, and financial resources to intervene in Central Asia and the Middle East through NATO and the UN. Perhaps the European powers are alienated from participating in a geopolitical arena dominated by an arrogant and antagonistic US, but in so doing they've begun to abdicate their role in forging a common global destiny in the liberal model.
If Europe is serious in following the lead set forth by Habermas, member states of the EU should revitalize their participation in the UN and meet the minimum staffing and funding requirements dictated by NATO membership. Until then, the European intellectual tradition will have rational and moral authority, but little practical role.