POD: The Spanish 1820 rebellion doesn't happen, the Spanish army overwhelms Colombian forces. While low level fighting continues for years. Bolivar can't attack Peru from the north, the Chilenean forces San Martin leads from the south are defeated by loyalist forces in Peru, as the loyalists aren't facing a two front war.
Peru remains loyalist, Colombia is a toss up. Chile, Argentina, Paraguay and Uruguay might remain independent if the Spanish are bogged down in Colombia, but Brazil might end up annexing Uruguay as Argentina might not feel comfortable in getting in a war with Brazil with Spanish armies still operating in the Upper Peru.
EDIT: Oops, checked you wanted a POD in the 18th century, not the 19th