Thanks for your question regarding internal and external factors of the HRM environment. These are two of the key considerations in HR for success, therefore there is a level of constant moderation necessary in order to ensure that HR strategy is constantly and consistently optimal, based on such circumstances.
In terms of external factors, there is a lot of competition in terms of recruitment so HR is effected by the company's ability to seek out employees. Smaller companies will have to work harder to find suitable and adequate employees. Job fairs must be attended and recruitment materials will need to be developed in order to secure this.
Internal factors also greatly effect the HRM environment. For example, some companies prefer to hire within, or promote the staff they already have. If such is the case, then it is HR's job to ensure that all applicants are ready for promotion, by providing adequate training within a set time frame so that no position will go unfilled.
These are just some of the internal and external factors in the HRM environment.
I hope this answers your question.