The late Cambridge theoretical physicist and cosmologist Stephen Hawking declared that the 21st century will be the century of complexity.

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Why should we care? Today's most pressing policy challenges - great power conflict, economic dependency, climate change and other non-traditional threats such as pandemics - are all complex problems. The challenges of complexity exacerbate the global shifts and diffusion of power, including the effects of the so-called Fourth Industrial Revolution. Together they create a level of uncertainty for policymakers that they cannot ignore.

Governments around the world must cope with the twin effects of shrinking policy space and the interconnectedness of policy issues they cannot control. The repercussions for the analysis and design of foreign and strategic policy and global public policy are profound. To be successful, policy-makers must be innovative and adaptive. Yet, the common reaction to complexity and uncertainty is to seek refuge in over-simplification, tactics, and process. Thus, the urgent need -- for governments, corporations, international institutions and other international actors – is to practice diplomacy and statecraft with a renewed emphasis on strategy.

But strategising is difficult in a complex world. It requires a sea-change in strategic imagination and policy mindsets. We tend to think in terms of causality – X causes Y. Yet complexity implies non-linearity, and therefore requires thinking in terms of systems. Complex systems, like those found in cities or the human body, are dynamic, involve numerous moving parts, and are hard to predict. Understanding a complex system not only requires analysing the behaviour of the constituent agents but also how they interact with each other, and how this relates to the functioning of other parts of the wider system.