While I don't believe that during the decolonization process Britain and France intentionally created a knowingly unstable state, policies implemented during colonial rule to make administration easier had the effect of destabilizing states in the long term. Either as an intentional policy (such as the Germans and Belgians intentionally widening the ethnic divide between Hutus and Tutsis, and putting the Tutsi minority in privileged positions) or as the result of practical considerations or ingrained biases (the promotion of christians to positions of power in colonial Nigeria), most European colonial governments used divide and rule policies to help maintain their positions. Minority groups were given special treatment and effectively turned into European clients, focusing the resistance of the majority population on these minority groups rather than on the overall colonial governments, and making these minorities beholden to the colonial power. Existing internal divisions were exacerbated, intentionally or unintentionally, for the benefit of the colonial regime, but not for the purpose of destabilizing that state post-independence.

Interestingly, despite Iraq's modern history of sectarian violence, Iraq was not an example of this divide and rule policy. While it has been popularly claimed that "Iraq" was a complete fiction, the three Ottoman provinces that made up modern Iraq (Mosul, Baghdad, Basra) were frequently governed together, including becoming de facto independent for most of the 1700s under a Mamluk dynasty. Aside from making up most of a historical and geographical region (Mesopotamia), they shared a hugely important common economic link of the Tigris and Euphrates rivers, and were in turn isolated from the Levant and Anatolia by deserts and mountains, respectively. So geographically and economically, it made sense for Iraq to have (roughly) its modern borders, as artificially dividing up the heavily interconnected regional economy of Mesopotamia didn't make any sense.

Secondly, though the region's ethno-religious divisions are obvious today, they weren't obvious in 1918. There was very little sense of a Kurdish national identity in 1918, and aside from a few intellectuals, most Kurds still lived in tribal societies, remote from state authority. "Arab Nationalism", as it is modernly conceived, itself was in its infancy in 1918. Furthermore, the Ottoman provinces that make up modern Iraq do not, as some people have claimed, represent an attempt to form ethno-religiously homogenous provinces. The divisions were simply based on Iraq's three major cities: Mosul, Baghdad, and Basra, and each province was very mixed, especially Mosul (Sunni-Arabs and Kurds) and Baghdad (Sunni and Shia Arabs).

Finally, at the outset of Iraq's creation, there was an attempt to use divide and rule--using the region's christian minorities. Assyrian and Armenian Christians were recruited to the "Iraqi Army" in the pre-independence period, and these minorities, beholden to Britain for their continued positions of power, could be counted on to fight to maintain British rule.

The modern sectarian conflict in Iraq can be traced to policies of the independent Iraqi government, especially the Baathist government, which limited political power to Sunni Arabs and violently repressed Kurdish and Shia groups.

In contrast to Iraq, the French, in their Mandate for Syria and Lebanon, intentionally used a divide and rule, with results that can especially be seen in Lebanon today. Upon taking control of Syria, the French faced a strong Arab nationalist backlash, and had to fight a brief war to secure their hold over the region. In response to this nationalist rebellion, the French divided Syria-Lebanon into the states of Aleppo, Damascus, Alawite, Druze, and an expanded Lebanon. Although Aleppo and Damascus were united a few years later, the other autonomous regions were kept separate from Syria proper. While there have been some effects of this today, most notably with the influence of Alawites in the Syrian regime in the current civil war, the most notable effects were in Lebanon.

Before French rule, the Ottomans had intentionally (after a sectarian conflict and heavy prompting from European countries, especially france) separated the population of Lebanon. The Maronite Christian population was given a special administrative division called Mount Lebanon, while Beruit and the northern and southern parts of modern Lebanon were made a separate province. After the French took over Syria, in conjunction with Maronite leaders, "Mount Lebanon" was expanded to include most of the province of Beirut and part of the province of Damascus, both of which had minority populations of Maronites and Shia majorities. The new Lebanon was roughly equally Christian and Muslim, with the Maronite Christians emerging as French clients, loyal to Paris and dependent on France to ensure their political power. Once the French left the region, Lebanon was now very divided along sectarian lines, and those divisions have resulted in conflict.

It really varies from state to state, but in some cases absolutely. My go to is the decolonisation of Guinea in 1958.

In 1958, Guinea somewhat unexpectedly voted to become independent (the other nine French colonies in West Africa voted against independence, hence the surprise). On leaving, the French administration went so far as to tear out the national telecommunications network, leaving the new government with no way of effectively communicating throughout the country [1]. Clearly, in this case, there was clear intention to punish and destabilise Guinea for their perceived rebelliousness.

The Belgian administration in Congo might also fall under this category. Belgian Congo was horrendously undereducated to the extent that, at independence in 1960, the nation boasted fewer than thirty university graduates [2]. This isn't necessarily a deliberate attempt to undermine the stability of a new state, but it certainly shows a kind of deliberate underinvestment in education that was designed to maintain a weak and divided population. Their later support for seccessionists in copper-rich Katanga province also falls into this category: not a direct effort to undermine Congo so much as a desire to preserve Belgian interests even at the expense of undermining Congo.

On the other hand, there were also examples of slow and managed transitions, for example Ghana, where Britain left a profitable and well-organised colony [3]. In part this was due to the length of time between the essential acceptance of eventual Ghanaian independence with the election of Nkrumah in 1951, and independence itself in 1957. Similarly, Kenya can also be seen as a comparatively managed transition.

Of course, I don't want to create the impression that the French were the ones setting up new nations to fail while the British weren't. In fact, France's continued commitment to 'Francafrique', while clearly neo-colonialism, does entail a commitment to ensuring the stability of West African client states which has seen French troops deployed to support governments across West Africa. Similarly, Britain's 'profitable' colony of Ghana faced economic collapse due to British economic mismanagement which tied economic performance closely to the price of cocoa beans.

Ultimately I'd say in the totality of my reading it seems that there were comparatively few deliberate efforts to set up states to fail after independence. Nonetheless, decolonisation often led to severe administrative burdens caused by colonial management, for example under-education, wildly unequal land distribution or the entrenchment of ethnic divides.

In short, colonialism wasn't bad because countries took revenge on decolonising states, but because it allowed and encouraged a series of policies which created imbalanced economies and unstable political systems.

[1] E. Schmidt, Cold War and Decolonization in Guinea, 1946-1958, (Ohio University Press, 2007) [2] D. Gibbs, “The United Nations, international peacekeeping and the question of ‘impartiality’: revisiting the Congo operation of 1960”, Journal of Modern African Studies, (2000), p. 362 [3] British Documents on the End of Empire: Ghana (Part I), R. Rathbone ed., (HMSO, 1992), pp. 66-67, 71, 129

a lot of the problems were unintentional, for example when Britain gave up the colony it would often remove all the Colonial Office and Foreign Office documents along with a lot of other official papers, these contained key information necessary for governing the country. The Administration of the colony could (depending on quickly the decolonization took place) collapse with the withdrawal of all the British nationals (and minorities) who were given the most important postings in government. (however this was not always the case it depends on whether the colony was decolonized or 'abandoned')

Ideally de-colonization would take place over a number of years (like it did in Malaya) with continued support until the new states government was firmly established. Malaya is probably a good example of this, the new Malay administration was gradually given more and more power and benefitted from continued British support during its Civil War (however the treatment of Chinese minorities often left much to be desired by today's standards).

However this often was not the case, which meant that a weak and ineffective government was established then Britain withdrew nearly all support basically removing the rug from beneath their feet. This was due to the fact there was huge pressure (political/military forces within colonies, political pressure in the UK and political pressure on the international stage) to withdraw from colonies, and limited funds to continue to support former colonies.