Colonialism
Colonialism is the theme that looms largest over A Bend in the River. Salim was from India, a country that was colonized by the British in 1858. Early in life, he immigrated to an unnamed country in Africa which was likewise colonized by a European superpower that desired the subjugation of the country's people and profound wealth. Throughout the novel, Naipaul shows the lengths to which those European powers went to maintain their power and order. Along the way, he offers a sharp rebuke of colonialism and the impact that it has had on countries across the world, including his native Trinidad and Tobago. For instance, Naipaul illustrates the brutal lengths many colonizers went to after Salim's village became violent. For days and perhaps weeks, Salim's village was lawless and violent. However, after the soldiers of the colonizing country came to the village, the order was quickly and brutally restored. In the end, if there is no order in a colonized country, things cost more for colonizers in terms of security and other related costs (like medical care and food costs), and the ability for colonizers to make money—perhaps the biggest reason they became colonizers in the first place—is impaired.
Romantic relationships
Initially, Naipaul reveals that Salim, the main character and protagonist of A Bend in the River, doesn't have experience with women and romantic relationships outside of the few times he visited prostitutes. However, Salim longs for a loving and romantic relationship with a woman and works hard to find a woman with whom he connects. He finds that initially with Yvette, a woman who is much younger than him but who excites him tremendously. However, because of Salim's lack of experience and his ostentatious behavior cause their romance to fizzle before it truly begins. Eventually, though, Salim meets his business partner Nazruddin's daughter, with whom he falls deeply in love.
Quickly, Salim learns that romantic relationships need to be cultivated. They also don't happen without the exertion of some effort on both sides, something which Naipaul stresses through the inclusion of this theme. Having a relationship with someone—romantic or otherwise—shouldn't come easy and takes effort to cultivate and make last.
Islam
Salim, the protagonist and main character of the novel, is an ethnic Muslim from India. Early in life, Salim moved to a remote town in a small country in Africa, where he was one of the few Muslim people. Despite not being around many people who adhered to Islam, Salim continued to dutifully practice his religion throughout his life, observing holidays and following customs even when it would have been easy to ignore them. Naipaul shows the important role that religion plays in the lives of its adherents and how transformative it can be in a person's life. Salim, for instance, pursues a relationship with Yvette (rather than visiting prostitutes) because of his religion, thus making his life better and more fulfilled.