Final answer:
The information provided does not specify a particular convention held in Kansas City, nor does it indicate when it was held for the 'last time.' Further clarification from the student is needed to accurately answer the question.
Step-by-step explanation:
The question seems to be asking about a specific historical convention held in Kansas City, but it does not provide a clear context or specific details as to which convention it is referring to. From the provided information, there are several historical events concerning Kansas, such as the sacking of Lawrence, the Lecompton Constitution, and various conflicts related to the proslavery and antislavery movements leading up to the Civil War. However, there is no mention of a specific 'convention' in Kansas City or a date for the 'last time' such an event was held.
It appears that there might have been confusion or a typo in the original question, as the information does not align with a known historical convention in Kansas City. To provide the most accurate assistance, further clarification or details regarding the specific event in question would be necessary.