I hadn't known that Keynes had a brief protectionist period:
Keynes's 1933 writing on "National Self-Sufficiency" marked the furthest point of his departure from the idea that free trade promotes peace…"National Self-Sufficiency" argued against free international mobility of goods and capital on the grounds that such mobility could endanger peace; that gains from the international division of labour had diminished; and that such mobility placed individual economies 'at the mercy of world forces.' Keynes proposed a gradual move towards greater 'economic isolation' and 'national self-sufficiency.' in goods and finance. His motivations included his desire for Britain to fight unemployment with expansionism, which required free from 'interference from economic changes elsewhere'; and his new belief that 'economic internationalism' was inimical to peace.
That is from Donald Markwell's generally quite interesting John Maynard Keynes and International Relations: Economic Paths to War and Peace. And you will find the essay here. Keynes, of course, did snap out of that phase. One thing I learned from this book is that international relations is the key topic for tracing the evolution of Keynes's thought over his entire career.