When I add an event to iCalendar on my computer with no alert, why does it show up on my phone with an alert?

I use iCalendar often for work, so I add a lot of events at one time on my computer and sync them with my other devices thru iCloud. When I add events on my MacBook I make sure that they do not have any alerts. When they sync to my iPhone, for some reason they have alerts attached to them. The alerts only show up on my phone, they do not show up on my computer. Why is this happening and how do I prevent it? Obviously I can go thru all the events on my phone and turn off the alerts one by one, but I literally have 100s of events each week and will go crazy if I have to go thru each one. There has to be a way to stop this from happening. Please help.