There are many connections between the countries of Ivory Coast and Sierra Leone.
Historically, both nations were major ports in the Portuguese slave trade. Eventually the French colonizes Ivory Coast, but Sierra Leone was colonized by the British. When the slave trade ended, they both became sources of African trade goods for Europe, as well as sources of raw materials.
More recently, the countries have been united by issues revolving around conflict diamonds. Ivory Coast has been a major smuggling route for diamonds from Sierra Leone because it had a legitimate diamond industry. When their own diamond trade was shut down by the UN in 2005, the Ivory Coast began secretly smuggling its diamonds out through other nations, such as Sierra Leone.