Israel was buying weapons from the US in the 90’s and sources in the media got word of it. A whole debate developed whether or not this should be supported and what the implications were. (focusing on an activity)

According to our sources of information, Israel bought weapons from the US in the 90’s. (Fact – this is informative, there is no need to elaborate) 

They were going swimming a lot last week, I don’t know why exactly, maybe they’re trying to get in shape. (An unusal activity in a specific time frame)

They went swimming every Friday. (This activity happened regularly every Friday)

He was working as a substitute Hebrew teacher that week, apparently there was a special project that he took part in. (unusual and temporary activity in a specific time frame in the past) 

He worked as an English teacher back then. (A permanent situation in the past – it is his regular job and cannot be regarded as temporary or unusual.)

He was talking on the phone, reading the news and having breakfast at the same time. (simultaneous actions in the past)

He got up at 8:00, washed his face, got dressed and went to work. (chronological actions in the past)

I was thinking of buying a new car but eventually I decided not to. I had too many expenses and I needed to be frugal. (A thought process that was happening in a specific time frame – notice how we have to add more information about what happened around that activity for the structure to make sense.ו) 

I thought you were right. (The word “think” in the sentence does not represent a thinking process but a general position about a certain subject – it is strictly informative)

I was talking to my friend on the phone when the doorbell rang. (A progressive activity in a time frame that was interrupted by another action – notice how the action we focus on is in progressive structure and the interrupting action is in the simple structure. ) 

I talked to my friend on the phone, the doorbell rang and I opened the door. It was a delivery. I signed the package and closed the door. (Chronological actions in the past – it is apparent, by the use of the simple structure, that I first finished the conversation with my friend and only then did the doorbell ring. We will always use the Past Simple structure when we wish to relate to chronological actions. )