This question is very generic, and it is almost impossible to answer this correctly without knowing what the external system is, and what kind of integration you are looking at. In theory, it is possible to integrate any system with Salesforce via ETL tools, or via webservices, or sometimes using built in bespoke adaptors. But without a proper context it is not possible to confirm either way.
This question is very generic, and it is almost impossible to answer this correctly without knowing what the external system is, and what kind of integration you are looking at. In theory, it is possible to integrate any system with Salesforce via ETL tools, or via webservices, or sometimes using built in bespoke adaptors. But without a proper context it is not possible to confirm either way.
Hope this helps!