Back in November 2014 I was lucky enough to take part in a conference at RMA Sandhurst as part of OPERATION REFLECT. This Franco-British operation aims to identify lessons for modern militaries from the First World War. It also included a conference at RUSI in July and a week-long staff ride to the Western Front in September. The November session sought to pull together the most important points arising from the work of the previous few months. One major theme running through the day was the nature of alliances and their impact on operations. As is often the way of these things, we had little time properly to define what we meant by ‘alliance’, much less to review the broad range of alliance relationships which existed at various times, even just between the British and French on the Western Front. In the months since November, events, most of them too tedious to rehearse here, have conspired to give me rather more time to think than usual and I thought it might be worthwhile to preview some thoughts on alliances and the First World War here.
First, some definitions and distinctions. From time to time, states come together to deter or fight others. Motivations for doing so vary. They may be negative (designed to avoid an outcome parties view as undesirable) or positive (aiming to progress towards either shared objectives or the promotion of shared values). They may be a mixture of both, and they may of course involve any number of compromises and trade-offs. In 1914-18, for instance, Britain and France were prepared to ally with Russia despite liberal distaste for Tsarist values. While a ‘coalition’ is ad hoc and relatively informal, an ‘alliance’ suggests a more formal relationship. It might be governed by a treaty which outlines the rights and duties applying to members: or might not. It probably possesses some mechanisms for shared decision-making, although these may be rudimentary or highly developed. It might be the product of peacetime diplomacy, or purely the outcome of wartime evolution.
Friction is inevitable in any coalition/alliance relationship, but the level of that friction varies according to four external variables. The more of each of these factors there is, ceteris paribus, the less friction results:
1) Homophily: the more closely two militaries, or the members thereof, resemble each other, the more closely they tend to be able to work. Shared language and culture obviously can enable easier working relationships, but won’t necessarily do so, as the case of Robert Nivelle in 1917 showed. Inter-operability can work in many other dimensions as well, of course. One is very unlikely to have time and space to improvise this in wartime.
2) Congruence of interests/objectives: the more alignment exists between partners in terms of desirable end-states towards which they are working, the more likely they are to be able to agree.
3) Urgency: the more critical it is that partners work together, the better. Petty frictions get overlooked and divergences are resolved most rapidly when the stakes are highest and time most pressing.
4) Integrated command: the more established the mechanism for reaching and disseminating coalition/alliance decisions, the more smoothly work gets done. The more ad hoc the decision-making process, the more opportunities exist for deliberate sabotage or by-pass, the less practice all involved have had of working together, and the less clarity there is around the chain of command.

If we look now at the operational level Franco-British relationship on the Western Front (and only there) in 1914-18, we can distinguish 5 main phases:
A) August-October 1914: The BEF and French army share a structure and approach to war but are socially very different in composition, often have no language in common and are thrown together into a war with a common enemy but no practice of working together and little opportunity for discussing and agreeing on common ends, ways and means. Distrust and confusion are rife. By the 4 September 1914 Declaration of London, GB, France and Russia agree ‘no separate peace’ but no provision is made for joint strategic direction, much less military command.
B) October-November 1914: First Battle of Ypres: Foch manages to achieve a remarkable feat of integration with British and French units fighting together as one army. This is achieved partly through Foch’s own qualities of leadership, largely because the threat is so overwhelming and urgent that there is no alternative. When the threat subsides, cooperation deteriorates and the relationship deteriorates into…
C) December 1914-June 1917: The BEF is very much junior partner in a coalition which shares fundamental values and vague objectives but has only limited ideas about how to achieve the latter. Although levels of goodwill fluctuate, the relationship is largely characterised by distrust and mutual lack of respect. Coordination of decision-making is ad hoc and the experiment of giving Nivelle authority as supreme commander is immediately undermined, first by Haig’s opposition, soon thereafter by defeat on the Chemin des Dames.
D) June 1917-March 1918: Failure of the Nivelle offensive and the rash of unrest, although quickly cleared up by Pétain, gives the British more weight in the coalition, which they use to launch the Ypres offensive. The Supreme War Council at Versailles (from autumn) offers a formal forum for joint decision-making but rarely moves beyond being a talking shop.
E) March-November 1918: The Spring Offensives come close enough to breaking the coalition apart that Foch is given the backing of national governments to act as supreme commander. He relies, however, on persuasion rather than giving orders to get his way. The accelerated arrival of the Americans (as soldiers of an Associated Power, note, not an Ally) makes for a stronger and more balanced effort which finally prevails over the (by now much weakened) enemy.
(You might feel that some of those phases correspond with stages in operations in Iraq or Afghanistan, but I couldn’t possibly comment.)

To summarise: the coalition worked most smoothly in phases: B, when the urgency was greatest; and E, when urgency was high, the objective clear and means most readily available. By 1918 both BEF and the French army had grown together and coalition had moved closer towards a tight formal alliance, even if it was still a long way short of the remarkable integration achieved under Eisenhower with SHAEF. Which was itself still far from frictionless, but that’s a story for another day…